①金属单质 ②碱性氧化物 ③碱 ④非金属单质⑤酸性氧化物 ⑥酸
A：①②③
B：①④⑥
C：②⑤⑥
D：全部
The chief engineer of the high-speed railway ________ Shanghai to Beijing always devotes most of his time ________ his work.
