A:蛋白质
B:脂肪
C:糖类
D:无机盐
I saw him in the library yesterday. He ________ a book at that moment.
下列说法正确的是( )
如图所示,甲、乙两支完全相同的试管.分别装有质量相等的液体.甲试管内装水,乙试管内装煤油,两试管液面相平.设液体对两试管底的压强分别为P甲和P乙,则( )