“此”在“吾何以知天下之然栽。以此”中是什么意思？（）
A.德
B.道
C.权
D.相
参考答案：B
Their teacher was ill, so they sat in the classroom__________. [ ]
A. in silent
B. in silence
C. silent
D. silence
有哪几种人防专业队伍？
