1-David has made great progess recently ---,and --A.So he ha

1-David has made great progess recently -__,and __A.So he has;so you are B.so he has ;so have y1-David has made great progess recently -__,and __A.So he has;so you are B.so he has ;so have youC.so has he;so have youD.so has he;so you have求解释,另外2、The maths problem is to difficult for me to work (it) out要用it么