He worked out such different questions at a very young age.— Oh, he ______ a very smart student then.

下列与“难为俗人言也”中“为”的意义和用法相同的一项是（　 ）

______ do you go shopping, Mary — Twice a week.

Many people believe that hunger is only a problem in the developing countries.________，it is a problem all over the world.

help you—I’d like to buy a presentfor my father’s birthday,at a proper price,but of good use.