这句不知道到底是什么意思

20. An array of tax incentives has led to a boom in the construction of new office buildings; so abundant has capital been for commercial real estate that investors regularly scour the country for areas in which to build.

(A)  so abundant has capital been for commercial real estate that

(B)  capital has been so abundant for commercial real estate, so that

(C)  the abundance of capital for commercial real estate has been such,

(D)  such has the abundance of capital been for
                commercial real estate that

(E)   such has been an abundance of capital for
                commercial real estate,

Choice A is best. The construction so abundant has capital been... that correctly and clearly expresses the relationship between the abundance and the investors' response. In choice B, the repetition of so is illogical and unidiomatic. Choices C, D, and E alter somewhat the intended meaning of the sentence; because of its position in these statements, such functions to mean "of a kind" rather than to intensify abundant. Choice D awkwardly separates has and been, and the omission of that from C and E makes those choices ungrammatical.

牛人帮我解释一下吧，我没看懂这句的意思

多谢

32. Some buildings that were destroyed and heavily dam­aged in the earthquake last year were constructed in violation of the city's building code.

(A)  Some buildings that were destroyed and heavily damaged in the earthquake last year were

(B)   Some buildings that were destroyed or heavily damaged in the earthquake last year had been

(C)  Some buildings that the earthquake destroyed and heavily damaged last year have been

(D)  Last year the earthquake destroyed or heavily
                damaged some buildings that have been

(E)   Last year some of the buildings that were
                destroyed or heavily damaged in the earthquake
                had been

Choice B is best. Choices A and C illogically state that some buildings were both destroyed and damaged; or is needed to indicate that each of the buildings suffered either one fate or the other. In using only one verb tense, were, A fails to indicate that the buildings were constructed before the earthquake occurred. Choices C and D use the present perfect tense incorrectly, saying in effect that the buildings have been constructed after they were destroyed last year. Choice E suggests that the construction of the buildings, rather than the earthquake, occurred last year, thus making the sequence of events unclear. Only B uses verb tenses correctly to indicate that construction of the buildings was completed prior to the earthquake.

这个题中，我不明白为什么要用过去完成时