( )I am,weak in English.I don't know -.

( )I am,weak in English.I don't know _.A.what to improve B.how can I improve it C.how improve D.howI can improve it.( )Millie can't ride a bike very well.Please don't jump on her bike suddenly while she is riding,or she will _.A.fell down B.felled down C.felt down D.fall down