Whenever I think of my childhood, I'll always feel that the period of free time seem to have passed ________

A．for ever

B．by and by

C．little by little

D．in a flash

疑病症的主要症状是（）

A.害怕会患上疾病

B.害怕疾病的传播

C.害怕与有疾病的个体接触

D.害怕目前已经患病