A:as twice
B:twice much
C:twice much a
D:twice as much
— I'd love to, but I think we shouldn't __________ our progress. We also have a long way to go.
人体的肌肉主要是有蛋白质构成的,但是骨骼肌、心肌、平滑肌的功能各不相同,这是由于( )