心室的血液充盈主要依靠心房的收缩。
参考答案:错
_________ is a famous waterfall in Canada.[ ]
A. Huangguoshu Falls
B. Detian Falls
C. Colorado Falls
D. Niagara Falls
某种商品若按标价的八折出售,可获利20%,若按原标价出售,可获利( )
A.25%
B.40%
C.50%
D.66.7%