请教98年8月北美的几道语法题

9. The dawn redwood appears______some 100 million years ago in northern forests around the world.

A. was flourished

B. having to flourish

C. to have flourished

D. have flourished

很显然，这道题是考appear的用法，appear to do/ appear to be done.所以答案是C，但是我有个疑问，100 million years ago 前面可以用现在完成时have flourished吗，我们不是在初中就学过看到ago 前面就应该用过去时的吗？

13.______of large mammals once dominated the North American prairies the American bison and the pronghorn antelope.

A. There are two species

B. With two species

C. Two species are

D. Two species

这题不难，答案是D。但是我死活查不到prairies是什么意思，请高手指点一二

28. Each chemical element is characterized to the number of protons that an atom of that  element contains, called its atomic number.

答案是B。应该是characterized by,表被动。但我觉得its也有问题，去掉更合理，最后一句做后置定语。还有that an atom of that element contains怎么解释啊，是做protons的后置定语吗，我总觉得别扭，是不是原题有错误啊，and an atom of that element contain，是不是更合理些？

1. 可以

2. prairie大草原

3.题目没有错。that an atom of that element contains意思是：那种元素的原子所带的

called its atomic number被称为这种元素的原子序数, it指代前面的元素chemical element

I got it, thanks a lot