已知X、Y、Z、W均为中学化学中常见的单质或化合物，它们之间的转

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问题选择题

已知X、Y、Z、W均为中学化学中常见的单质或化合物，它们之间的转化关系如图所示（部分产物已略去）。则W、X不可能是

答案

选择题

He gave us another piece of advice, ________ of great help to the research work.

A．which I think is

B．which I think it is

C．I think which is

D．I think it is

单项选择题

儿童好发

A．骨肉瘤
B．骨肿瘤
C．髋关节结核
D．急性血源性骨髓炎
E．化脓性关节炎