缺铁性贫血早期最可靠的依据是
A．运铁蛋白饱和度降低
B．血清铁蛋白降低
C．红细胞内原卟啉增高
D．血清总铁结合力增高
E．血清铁减少
参考答案：B
How can you expect him to make any improvement________ you never give him a chance to have a try?[ ]
A. unless
B. when
C. until
D. even if
手工电弧焊焊接和高强度螺栓连接相比，手工电弧焊具有（）的特点。
A.构造简单、加工方便
B.易于操作
C.节约钢材
D.不削弱杆件截面
E.对疲劳不敏感
