The machine has been used much too long.  ________it doesn't work well sometimes.  [ ]

A. It's no wonder that

B. There's no doubt if

C. It's unlikely

D. That's because

免疫组织化学过程不包括（）

A.过氧化氢处理切片

B.胰蛋白酶消化

C.非免疫血清封闭

D.杂交

E.滴加第一抗体