С. надо раскрыть скобки и поставить глагол в present perfect. вот предложения: 1) our son (learn) how to reed. 2) scientists (split) the atom. 3) english (become) one of the most popular courses at the university. 4) i think i (see) that movie before. 5) joan (learn) two foreign languages. 6) you (see) that movie? - i (see) that movie twenty times. 7) people (travel) to the moon. 8) james (not finish) his homework yet. 9) the rain (not stop). 10) she (be) in england for six months.