所谓元素是指具有相同核电荷数(即质子数)的同一类原子的总称,目前只发现109种元素,在地壳里分布最广的是( )元素。
A.铁
B.锰
C.碳
D.氧
参考答案:D
— I haven’t got the reference book yet, but I’ll have a test on the subject next month.
— Don’t worry. You ________ have it by Friday.
A.could
B.shall
C.may
D.must
策略技巧的应用规律和效果有哪些?