使用如图所示的装置匀速提起重物G,所用的拉力中( )
A:F1最大
B:F2最大
C:F3最大
D:一样大
1500÷500=____
9300÷3=____
20×50=____
1000÷50=____
To be an artist is not easy, but sometimes dreams can be a rich source of ________—for an artist.