下列说法错误的是（ ）。
A．含氧化合物不一定是氧化物
B．纯净物都是由一种物质组成的
C．由一种元素组成的纯净物不一定是单质
D．质子数相同的微粒不一定属于同种元素
答案：C
A项，氧化物是指由两种元素组成的化合物，其中一种元素为氧元素的化合物，所以含氧的化合物不一定是氧化物，如KMnO4等，A项对；B项，纯净物是由同一种物质组成的，B项对；C项，由同一种元素组成的纯净物是单质，如O2、H2等，C项错；D项说法是正确的，微粒包括分子、原子、离子等。
完型填空。（每小题0.5，计5分） Perhaps you ride a bicycle to school. Riding a bicycle can be great fun. Do you know how to ride a bicycle 41 ? Careful boys and girls learn to ride their bicycle well 42 they go out on the road. How can you tell 43 you are a good rider or not? If you can ride a bicycle in a straight line, you can ride well. If you can’t, you should practice riding 44 a safe place. To be safe on a bicycle, you 45 to use both hands and both feet. 46 your feet on the pedals (脚踏) and your hands on the handle bars (把手) at all times. Do you have a basket on your bicycle? If so, put your books and other things in the 47 . You know that your bicycle is built for one person. It is not safe to carry anyone 48 you. 49 is this so? Keep 50 safe by safety rules when you ride on a bicycle.
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