A:①③
B:②④
C:①②
D:③④
同学们“测量并探究影响滑轮组机械效率高低的因素”,使用了如图所示的装置,下列说法正确的是(每个钩码重相同)( )
— They are eager for a great victory.
一 Work hard and I believe they‘’ll surely make it.