In the lecture, the professor told his students how to write an ______ of a graduate paper, expressing the main argument.
Vitamin D helps our bodies make a special chemical,and this special chemical,________,affects our brains,making us feel happy.
Some of us remain________at our computer for hours every day,forgetting moving our body.
—As a teenager,our son should have two or three hobbies to be really happy.—________,but how can he afford the time with so much homework every day?
We pursue happiness,thinking one day we will find it.But_________it by seeking it.
Some fruits are so easily harvested in this area that they are never of great________.