某元素原子的价电子构型为3d104s2,它属于第_______周期,是________族,________区元素,元素符号是_________。
四;ⅡB族;ds;Zn
—Tom, is this _____ book?
—No, it isn't. My book is in my bag. [ ]
A. his
B. you
C. your
液控单向阀一共有三个油口,正向油口、反向油口和()。