OE


As this passage implies, the sloth has a reputation for being slow and lazy, and the first missing word will reflect that. Fulsome is too negative for the neutral and descriptive tone of the passage; it means offensive to good taste or sickening. Lugubrious means mournful or gloomy and has nothing to do with the subject of the passage. This leaves you with phlegmatic, which means not easily excited to action or display of emotion and is the correct answer.
Given this, the second blank must refer to a lazy or inactive person. Virago means an ill-tempered, scolding woman eliminate it. Libertine is similarly irrelevant; it means a person who is morally or sexually unrestrained. Sluggard, however, fits perfectly; it refers to a person who is habitually inactive or lazy.
Finally, we know from the rest of the passage that sloths do not move frequently, so they must avoid physical activity. Inveigh against does not make sense; sloths do not protest strongly against physical activity, they simply refrain from it. There is also no indication that sloths go through an active period, so it cannot be that they wean themselves off (withdraw from) physical activity. The best answer is abstain from, which means to hold oneself back voluntarily.