甲在t时间内做功W,功率为Pl;乙在t时间内做功2W,功率为P2,则下列关系中正确的是( )
A:Pl<P2
B:Pl>P2
C:Pl=P2
D:无法确定
John: What do you do on Sundays?
Tom: I read books and watch TV. What do you do on Sundays?
John: I do my homework . What about you, Mary?
Mary: I clean my room and watch TV.
John: You're helpful.
在七大洲中,南、北回归线均穿过的大洲是( )
桌上倒扣着背面相同的5张扑克牌,其中3张黑桃、2张红桃.从中随机抽取一张,则( )