Can I say,<br/><br/>(a) They help their mother to prepare dinner / for dinner.<br/><br/>(b) Mrs Tang is teaching art now. <br/><br/>(c) The children are playing in / at the park. <br/><br/>(d) She combs her hair in front of the mirror. <br/><br/>(e) He ran very fast in the event. <br/><br/> He ran very fast in 100 metre event.<br/><br/>(f) She waves her hand with /to us.<br/><br/>(g) I skip the rope very well.