唾液的作用,不正确的是()
A.消化作用
B.清洁作用
C.吞噬作用
D.缓冲作用
E.排泄代谢物质
参考答案:C
Daniel is helpful. He often ______ first. [ ]
A. thinks over others
B. thinks of himself
C. thinks about others
D. thinks of others
数字微波通信中站距通常采用()
A.30km
B.50km
C.80km