Number 5 is the answer because it summarizes the topic of the paragraph.
The answer is A. tree. The plural form of tree is trees.
For the first question, the answer would be D. (It supports the idea that living in a foreign country is the smartest way to learn a new language)
D: Language researchers found that students who lived in a foreign country learned the new language sixty-five percent faster than students learning at home.
The counterclaim is something that counteracts the statement. Therefore, for the second questions, the answer should be B.
B: However, learning to play an instrument has been proven to improve grades and test performance.
It is false that reading a play rather than seeing it takes away all of its entertainment value. Both reading and seeing a play can be very entertaining, it has nothing to do with the medium.