缺铁性贫血的细胞形态学表现为()
A.小细胞低色素性贫血
B.小细胞正色素性贫血
C.正细胞正色素性贫血
D.大细胞低色素性贫血
E.大细胞性贫血
参考答案:A
某同学通过仔细观察发现生活中有很多简单机械,如:手钳、剪刀、镊子、扳手、钥匙等等.如图,当把钥匙插入锁孔开锁时,钥匙就相当于______(填“杠杆”、“轮轴”、“滑轮”或“斜面”),它是一个______(填“省力”或“费力”)的机械.
It is the first time I _____ visitors since I moved to London.[ ]
A. had had
B. have had
C. have
D. had