目前农业生产上盲目地使用化学肥料，造成土壤酸化、板结以及土壤污染，根据你所学的知识，你对农民的合理施肥的建议是 ____________________________   

—I think the man over there must be Bob.

-- It_______ be him. He has______ to Australia. 

A．can’t, gone

B．can’t, been

C．may not, been

D．mustn’t, gone