早古生代包括（）和志留纪，自六亿一千五百万年前的寒武纪初至四亿年前的志留纪末，延续时间达二亿一千五百年左右。
参考答案：寒武纪、奥陶纪
根据英文解释、汉语提示及句意，写出句中所缺单词。
1. May is my _________(忠实的) friend and I can share my problems with her.
2. My mum can cook _________ (tasty) meals. And the chicken tastes nice.
3. How many ___________ (语言) can you speak?
4. You must drive carefully because there is too much ________ (movement of cars) on the city road.
5. I don't want to watch TV this evening. I'll listen to music i_________.
有机物甲是一种包含有一个六元环结构的化合物，其分子式为C7H12O2，在酸性条件下可发生水解，且解产物只有一种。则甲的可能结构有
A．8种
B．11种
C．14种
D．15种
