1) I believe you.
2) The girls are singing together very well and l like it.
3) Who knows this story?
4) Her best friend can't swim.
5) Nobody can understand it.
6) He isn't speaking German, he is speaking Spanish now.
7) We hear the professot very well.
8) Is that dog going to give that cat a lesson?
9) He has two sisters and a btother. / He has got two sisters and a brother. (Оба варианта возможны, в Англии используют has got, а в Америке просто has)
10) Can you ride a motobike?
11) правильно