It is very kind ______ you to help me with my lessons. It is difficult ______ me to learn them well. [ ]

We should eat a balanced diet to keep healthy.

Harry Potter is an____book for children, but my cousin doesn’t seem at all_____in it.

China has _____ area of about 9,600,000 square kilometers, including Diaoyu Island(钓鱼岛) .

Your paintings are so great, David! When did you learn ______?—Three years ago.