0.000668用科学记数法表示( )
A.6.68×10-4
B.66.8×10-3
C.0.668×10-5
D.668×10-2
0.000668=6.68×10-4,
故选:A.
8. Most of us would rather send e-mail as it has____of the troubles of sending letters via the post office.
A.nothing
B.none
C.some
D.Either
二尖瓣腱索断裂的特征性超声发现是()
A.二尖瓣回声改变
B.左心室扩大
C.左心房扩大
D.二尖瓣反流
E.连枷样运动