只形成可溶性的抗原抗体复合物（）
A.前带
B.后带
C.前带或后带
D.前带和等价带
E.等价带
参考答案：C
A new survey shows that 54% of Americans do not take prescription medicines _______ though they are important to their health. [ ]
A. as they instruct
B. as were instructed
C. as to be instructed
D. as instructed
用于沙质河床的采样器，应能采集表面以下深度（）mm内的样品。
A、100
B、200
C、300
D、500
