胎盘的组成包括( )
A.膜、叶状绒毛膜、底蜕膜B.初级绒毛、二级绒毛、三级绒毛C.绒毛膜、羊膜D.胎盘、胎膜、脐带、羊水E.底蜕膜、包蜕膜、真蜕膜
参考答案:A
Americans eat_____vegetables per person today as they did in 1910.
A.more than twice
B.as twice as many
C.twice as many as
D.more than twice as many
稳定塔进料温度高时,使用下进料口进料;温度低时使用()。