单项选择题
Intelligent use of the muscles means that()
A．one always knows what his muscles are doing B．one performs simple actions without working C．one's muscles are used only to the extent necessary for each action they perform D．one improves muscular action consciously
单项选择题 Under a microscope , muscle cells appear to be ()
单项选择题 According to the selection more than half of a person's body is composed of()
单项选择题 Muscles are unique fibers, because they can ()
