He tried his best to make the novel( ),but it's difficult.

He tried his best to solve the problem,however difficult it He tried his best to solve the problem,______ difficult it w he tried his best to save the drown girl,but unfortunately s The young teacher tried his best,but he still could not make He tried to make his dog eat some meat ,but the dog didn't e He tried his best to solve the problem,_______difficult it w He tried his best to solve the problem __difficult it was 为什 He tried his best to slove the problem,_A___difficult it was ___difficult the problem was,he tried his best to solve it. He tried his best-[not show]it. he tried his best to make his classes live有一处错误, he is a little weak in this but he tried his best to catch u