新鲜蛋清有杀菌作用，这种作用在37℃的环境中可保持（）小时，温度越低，保持时间越长。
A、6
B、12
C、24
D、30
参考答案：A
Last month, the Japanese government expressed their thanks for the aid they ________ from China.[ ]
A. receive
B. are receiving
C. have received
D. had received
以下哪种细胞不是牙周膜中的细胞成分（）
A.成纤维细胞
B.成骨细胞
C.成牙骨质细胞
D.破骨细胞
E.成牙本质细胞
