24. The first decision for most tenants living in a building undergoing being converted to cooperative ownership is if to sign a no-buy pledge with the other tenants.
A. being converted to cooperative ownership is if to sign

B. being converted to cooperative ownership is whether they should be signing

C. being converted to cooperative ownership is whether or not they sign

D. conversion to cooperative ownership is if to sign

E. conversion to cooperative ownership is whether to sign
 
1, 简洁：（一级排除 A,B,C）
the phrase being converted is awkward and redundant, since the sense of process indicated by being has already been conveyed by undergoing.
 
2. 词法：(二级排除 D )
 表示是否用 whether, 表示条件用if
 及物动词+名词的形式 比 +分词的形式更加合理。uses the noun conversion, which grammatically completes the phrase begun by undergoing. undergo及物动词. 不能接分词.
 
3. 并列结构：
A is B，　 A/B 平行。 ==》 不定式可以作为名词性结构和名词平行。
The first decision 。。。 is whether to …..
to sign, that functions as a noun equivalent of decision
并列处处有!!!!系表结构是并列!!!!!!!!!!!!!!.

例句
140. It may be another fifteen years before spacecraft from Earth again venture to Mars, a planet now known to be cold, dry, and probably lifeless.
(A) again venture to Mars, a planet now known to be
(B) venture to Mars again, a planet now known for being
(C) will venture to Mars again, a planet now known as being
(D) venture again to Mars, a planet that is known now to be
(E) will again venture to Mars, a planet known now as being
 
C,E的将来时态不对, 排除
B的for being不对: for要么是目的关系, 要么是因果关系
for being 的意思是因为MARS是blablabla, 偶们才认识这个星球.---有点离谱
只有to be才是a planet的等价物!!!是名词性质!!!
里面的do又是动词 绝对比动名词being/doing好百倍
For being, as being都是介词短语, 不是名词性质的等价物!!!
D的that is多余, 不对
 
4．undergo 的用法v 经历[transitive not in passive]
if you undergo a change, an unpleasant experience etc, it happens to you or is done to you
The country has undergone massive changes recently.
He has been released from prison to undergo medical treatment in the United States.