用ELISA双抗体夹心法检测血清中甲胎蛋白(AFP)，应选择的固相包被物是()

A．已知AFP

B．酶标记AFP

C．抗AFP抗体

D．酶标记抗AFP抗体

E．待检血清

—Who are they?

—______.[ ]

A. It's Dave

B. They are Jim and Tom

C. They are Eli

D. That's a book