秋末树木落叶后,会发现植物体吸收水分的速度大大减弱,这主要是因为[ ]
A.光合作用减弱
B.呼吸作用减弱
C.蒸腾作用减弱
D.土壤含水量降低
答案:C
Mary must keep her mind on her medical studies now, so it would be years ______ she could think about marriage.
A.before
B.when
C.since
D.until
母线()后,应去毛刺。
A.落料
B.钻孔
C.冲孔
D.安装