推铅球技术有（）种
A.3
B.1
C.2
D.4
参考答案：A
He is only too ready to help others, seldom, ________ refusing them when they turn to him. [ ]
A. if never
B. if ever
C. if not
D. if no
蛋白质分子组成中不含有下列哪种氨基酸
A．亮氨酸B．蛋氨酸C．胱氨酸D．瓜氨酸E．丝氨酸
