()
A.
B.
C.
D.
参考答案:A
解析:
该数列可转化为:。其分母为积数列,分子为前一项的分子与分母之和,故空缺处应为所以答案选A项。
The students were excited when they knew they ______ out for a spring out the next month.
A.went
B.had gone
C.will go
D.would go
一质量为m=1kg的物体在水平恒力F作用下水平运动,1s末撤去恒力F,其v-t图象如图所示,则恒力F和物体所受阻力f的大小是()
A.F=8N
B.F=9N
C.f=3N
D.f=2N