企业的废旧物资，是企业沉重的负担。
参考答案：错
I hope we can do business together, and I'm looking forward with great interest ______ your call. [ ]
A. to receiving
B. for receiving
C. to receive
D. in receiving
直接凝集反应的抗原是（）
A.颗粒性抗原
B.可溶性抗原
C.半抗原
D.超抗原
E.异嗜性抗原
