党的基本路线的核心是“一个中心、两个基本点”。( )
参考答案：对
As a child, Jack studied in a village school, ______ is named after his grandfather.
A．that
B．where
C．what
D．which
如图所示，用动滑轮将重为600N的物体匀速提升4m（不计滑轮重和摩擦），求：
（1）拉力F的大小；
（2）拉力F所做的功．
