A:While
B:Whe
C:A
D:Since
Some exchange students _______ with their host families this time yesterday.
⑴read(现在分词)____ ⑵speak(现在分词)____
⑶go (单三式)____⑷story(复数形式)____
⑸have (单三式)____ ⑹do(否定形式)____
⑺begin(单三式)____ ⑻teach(单三式)____
⑼do (单三式)____⑽sing(现在分词)____
下列国家不是地跨亚欧两州的国家( )
若分式3x+5x-1无意义,当53m-2x-12m-x=0时,则m=____.