Such a difficult problem__that I don't know what to do with

Such a difficult problem__that I don't know what to do with I really don't know -----with it.A .what to do B.how to do 选 15.▲ such a difficult problem,I really didn’t know what to d I don't know ______.A what to do with it B what to do it wit I don't know what to do I don't know ___to deal with such matter?A:what B:how C:whic I really don't know ( ).A.what to do the next B.what to do i I really don’t know what to ______ about such a thing.A.say I really don’t know what to ____about such a thing. A.say B. The math problem is so difficult,I don't know __ A how to do 将I don't know what I should do to deal with the problem 改成简单 The bus _____start;I don’t know what to do with it.（b）