After ten years abroad, he still recognized his old colleagues ________ he set foot in China．

It is the prevention of disease______its successful treatment that has led to the rapid increase of the world’s population.

.—Jenny, I've finished my summer school classes.—Well, Chinese is _______ difficult to learn, isn't it?—It seemed that _______ at first. But after a while it starts to get easier. I got an A in the exam.

Not _______, the process of choosing names varies widely from culture to culture..

Broadly speaking, I would agree with Shirley, though not ________．