The sentence, as written, actually contains two separate phrases, with "When reaching for metaphors" being an introductory phrase. Introductory phrases always need to be set off by commas; therefore, the correct answer is "When reaching for a metaphor, authors often make their point more confusing."

The phrase "the first in the county in years" is an interrupting phrase, a clause that provides information to the sentence but is not crucial to the structure. All interrupting phrases need to be set apart from the rest of the sentence by commas; therefore, the correct answer choice is "The exciting political race, the first in the county in years, drew."

The phrase "In the first heat" is an introductory phrase in the sentence, one that conditions the meaning of the sentence (or in this case, the first part of this compound sentence), but remains apart from its structure. All introductory phrases need to be separated from the rest of the sentence by a comma. As this is the only punctuation error in the sentence as written, the correct answer choice is "In the first heat, every car spun out, and none of the racers finished the required four laps."

The phrase "for three years" is an introductory phrase, one that conditions the meaning of the sentence but is not part of the necessary structure of the sentence. All introductory phrases should be set off by a comma from the rest of the sentence. Therefore, the correct answer choice is "For three years, the fugitive lived."

The phrase "a giant canvas of the emperor" is an interrupting phrase, one that adds information to the sentence, but sits outside its main structure. Any interrupting phrase must be set apart from the rest of the sentence by commas. The only answer choice which appropriately places commas in the sentence is "The artist's masterpiece, a giant canvas of the emperor, had hung in the museum for centuries."

The phrase "a purebred champion" is an interrupting phrase, one that adds extra meaning to the sentence, but does not constitute a crucial element of its structure. All interrupting phrases must be set apart from the sentence by commas. The only answer choice that appropriately does this is "The dog, a purebred champion, was."

The phrase "a poor farmer" is an interrupting phrase, one that provides extra information but is not a crucial part of the sentence's structure. All interrupting phrases must be set apart from the rest of the sentence by commas. Therefore, the correct answer choice is "The lottery winner, a poor farmer, said."

"Although she was supposed to pick out one puppy to adopt at the animal shelter" is a subordinate or dependent clause. When you begin a sentence with a subordinate clause, you need to separate it from the independent clause with a comma.

The phrase "which went past his retirement" is an interrupting phrase, a phrase whch provides information to the meaning of the sentence but is outside the structure of the sentence. An interrupting phrase needs to be set apart by commas, making "For the next twenty years,which went past his retirement," the correct answer choice.

"Finding the best location" is an introductory phrase in the sentence, meaning that it conditions the action of the main portion of the sentence. All introductory phrases must be set apart from the main part of the sentence by a comma. The only answer choice that does this is "Finding the best location, the treasure hunters began digging furiously."