unknown 4道语法，请解析！谢谢！

lf

1，In 1987,molecular biologist L Mark Lagrimini of Ohio State University
cloned the gene  (in that ) codes for  (a type of )
peroxidase (found ) in tobacoo plants.



2,  It has ( long ) been known (as ) an entire cluster of galaxies
may sometimes (lie ) buried (within ) a vast dense ball of gas.



3,  The sudden expansion of heated air associated with lightning produces------------

often heard during a storm.


(A) thunder is the rumbling sound

(B) the rumbling sound,thunder is

(C) the rumbling sound,thunder,that

(D) thunder,the rumbling sound




4, The desire (to) species preservation is a primary (motivator) for (many) kinds of amimal behavior, (including ) reproduction.

desire

1. should be D were found


2 should be B     that


3.i think if C is" that is" then it's right. or D    the end should have " ,"    


4.motivator changed into motivation

KingKristy

3, should be D

lf

谢谢两位！

这4道题都是新东方机考模拟题里的。新东方给的答案是：

1，in that ----> that                                                

2, as -----> that

3, D

4, to ----> for



偶不是很明白这些题的语法规则，特别是第一题。可否给详细的解释？一后遇到他怎么可以比较容易的找出来？