We plant trees ________ and many of the trees are growing tall ________.

We plant trees ________ and many of the trees are growing tall ________.

A.year after year; year after year

B.year by year; year by year

C.year after year; year by year

D.year by year; year after year

答案及解析： C

year after year＝every year, year by year是指逐年变化．