The meaning of word in the parenthesis is the definition. Are there any clues as to why? "Living things thrive (live) in places where enviroment factors favor their survival."
This is a great question, as grammar is an important part of communication.
First, context is the key to all meaning. The word in parenthesis is live, which can mean thrive. In this context is certainly do. A few other words in the sentence make it so.
The word "favor" shows that the context is positive. In other words, the living thing will be able to do well, as the environment favors it.
The word "survival" also connotes the same point. Based on these words, we can be sure that thrive is well within the semantic range of "live."