— My son, who is now studying at a university, uses more than 3,000 yuan a month.

— Well, tell him to be economical.  After all, ______.

A．money doesn’t grow on trees

B．the morning sun never lasts a day

C．light come, light go

D．penny wise, pound foolish

制作样品的环节之一是（）．即在分好等级的烟叶内．先将质量中等的烟叶选出．再选质量较好（上限）和较差（下限）的烟叶

A.分类

B.分组

C.分级

D.分限