The correct answer is "gloomy." "Gloomy" means dark or dismal, so when describing the sky, it can mean that it looks like it is going to rain. "Bright" and "sunny" are opposites of the correct answer, and "hot" does not make sense in this sentence.

The correct answer is "humble." "Humble" means having a modest view of oneself; it is an opposite, or antonym, of "vain" and "boastful." The other words all mean the opposite of "humble" and do not make sense in the sentence.

Reclusive means characterized by seclusion. Someone who rarely leaves his or her house would be very secluded. While someone who is introverted might also prefer to stay home, reclusive is the better answer choice here.

Animals that are amphibious can inhabit land and water.  Therefore the best answer choice here is amphibious.

The only other answer choice that might work is versatile, yet that is not specific enough here, and therefore not the best answer choice.

A maniacal look is one that comes over someone when they become manic or crazed. A man in this state could be described as manic, and therefore his look could be seen as maniacal.

No other answer choice makes any sense. The man being described is certainly not elegant or impressive.  The man also cannot be encapsulated, or summarized, because that is nonsensical.  We also don't know if he is engaged, or busy, so that will not work either.

For the cancer to be in remission, the treatment must be working.  Therefore the correct answer choice is effective.  The treatment may or may not be intense.  It cannot be void or unreliable, as those choices would imply that the treatment is not working.  Competent is not as strong as effective, and it is usually used to describe people, not things.

"Passive" means not active or not actively participating. Since the dog was not joining the children in playing, he was being passive. "Playful" and "excited" are both opposites of the word for which we're looking, and "asleep" would not make sense in the sentence because it says that the old dog "preferred to watch the children play," and he couldn't do that if he were asleep. "Relaxing" might work, but it is not the best answer choice as an adjective here. So, "passive" is the correct answer.

A temperature change from seventy-three degrees to forty-five degrees is very large and noticeable. The definition of drastic is extremely severe or extensive, which is an accurate description of the change. 

A speech that is nearly two hours long would contain a lot of words, so one could accurately describe it as being "wordy," which means long or containing a lot of words and is used to describe written works or speeches.

The search was very involved and went far into her past, so it was very "extensive," or comprehensive and thorough.