下列各组物质中，属于同分异构体的是( )
答案：B
A项，二者互为同系物；C项，二者互为同系物；D项，二者所含元素不同，故分子式不同。
同义句转换
1. He concentrated his energies on study.
He _his energies _ study.
2. I must concentrate on my new task.
I must be _ _ my new task.
3. He fixed his eyes on his book and didn't notice we came in.
He his attention his book and didn't notice we came in.
柴油机的润滑系统主要包括机油泵、机油滤清器、机油冷却器和（）等。
