Помогите правильно выбрать форму глагола:1.The clock_____,it's time to finish your studiesA-strikes B-has stricken C-is striking2.They____ the problem now.A-understand B-are understanding C-have understood3.I___him today, but I...

Помогите правильно выбрать форму глагола: 1.The clock_____,it's time to finish your studies A-strikes B-has stricken C-is striking 2.They____ the problem now. A-understand B-are understanding C-have understood 3.I___him today, but I saw him yesterday A-didn't see  B-don't see C-haven't seen 4.He___this work before they came. A-had done  B-has done C-did 5.When we___the telephone rang. A-are talking  B-were talking  C-have a talk