While this sentence does not have anything grammatically wrong with it (the interjection is fine), it is wordy due to the inclusion of the interjection, which is somewhat unnecessary; therefore, it is best to omit it. The best choice is, "Some cities are now so big that we classify them as mega cities; the metro-Tokyo area has a population of over 36 million people."

This sentence contains a spelling error. "Wreckless" is not a word. It is spelled "reckless." The phrase "Studies have found that the safer we make things" is an example of an introductory phrase, explaining information necessary to the context of the sentence, but outside of the main sentence, grammatically. These types of phrases must be followed by a comma in order to separate them from the rest of the sentence, so the comma should stay where it is. The correct choice is, "safer we make things, the more reckless people act."

There are three errors in this sentence:

1. The absence of an apostrophe for "worlds"
2. The capitalization of the word "University"
3. The use of the passive voice in the verb "was established"

There should be an apostrophe before the "s" in "worlds" because it is possessive. Second, the word "university" should not be capitalized because the sentence is not referring to a specific university, but universities in general. Besides capitalization due to the position of a word at the beginning of a sentence, words are only capitalized when the word is a name or is referring to something specific that has already been named. Lastly, passive voice is a worse option than active voice in this case (the subject of the sentence should do the action of the sentence). The correct choice is, "Morocco is home to the world's oldest university."

This sentence contains two errors: 

1. "Running" is not a verb; it is a participle. Without a verb, this is not a sentence.
2. There is no need for a comma between "Benjamin" and the "verb."

The correct choice is, "Benjamin was running around his neighborhood." 

This sentence contains three errors:

1. The quote "What you do today can improve all your tomorrows" is not in quotation marks.
2. There is not a comma after "said."
3. The word "what" is not capitalized.

Note two things: quotations inside of quotations must take single quotation marks ('), instead of the usual double quotation marks. Additionally, ending punctuation should always appear within quotation marks. The correct choice is, "Veronica stated, "Ralph Marston said, 'What you do today can improve all your tomorrows.' " "

This sentence contains two errors:

1. The phrase "the...campaign was targeted at" is in the passive voice.
2. The phrase "the...campaign was targeted at" contains a dangling preposition.

The verb voice error is easily fixed by changing the words "was targeted" to "targeted," but you run into another error when rewording the sentence to fix the dangling preposition. In order to fix error number two, you must reword the sentence, but then that makes "who" the object of its clause, meaning you must also change this pronoun to "whom." The correct choice is, "whom the new marketing campaign targeted."

This sentence contains four errors:

1. The words Death of a Salesman need to be italicized since it is the title of a book.
2. A comma should follow the word "Miller," as it separates the main clause from the following quotation.
3. Quotation marks should be used from "When...pursuing."
4. The word "when," which should appear in the quote, should be capitalized since it is at the beginning of the sentence.

The correct choice is, "In the novel Death of a Salesman, Arthur Miller states, "When today fails to offer the justification for hope, tomorrow becomes the only grail worth pursuing.""

As stated in the sentence, the word "The Intelligent Investor" is the title of a book. Book titles should always be underlined or italicized. The correct choice is, "many regard the book The Intelligent Investor as the best book on investing."

All of the above choices are grammatically correct, but all but the correct option are obviously wordy. "He thought that everyone should be involved in politics" is the correct choice because it concisely states the same idea of all the other choices. None of the other choices add any substance to this sentiment (correct answer is always the most concise).

This sentence contains three errors:

1. Dangling preposition (for).
2. Sentence Fragment (second clause is incomplete).
3. Passive voice (he was respected).

The sentence needs to be reworded in order to fix these errors. Note that the correct sentence should always be in the active voice (i.e. the subject of a clause should do the action of the main verb). Additionally, prepositions should never end a clause. The correct choice is, "mistakes, people respected him for admitting them."