敦请给位高人帮我翻译一下,谢谢

清心_巧UID: 3199712

Indications are that the HDR resource base is very large. If an average geothermal temperature gradient of 22℃ per kilometer of depth is used, a staggering 13,000,000 quadrillion B.T.U.’s of total energy are calculated to be contained in crustal rock to a ten-kilometer depth in the United States. If we conservatively estimate that only about 0.2 percent is recoverable, we find a total of all the coal remaining in the United States. The remaining problem is to balance the economics of deeper, hotter, more costly wells and shallower, cooler, less expensive wells against the value of the final product, electricity and/or heat.
红色的部分不太理解,尤其是第一处.
对应下面这道题.我选了D答案是E.
According the passage, an average geothermal gradient of 22℃ per kilometer of depth can be used to
(A) balance the economics of HDR energy retrieval against that of underground hot water or steam recovery systems
(B) determine the amount of energy that will used for space heating in the United States
(C) provide comparisons between hot water and HDR energy sources in United States
(D) revise the estimates on the extent of remaining coal resources in the United States
(E) estimate the total HDR resource base in the United States
谢谢:)

caoys2012UID: 3182385

gradient of 22℃ per kilometer 后面直接跟的是算total energy,加上conservatively estimate才能算出remaining coal resources,所以光问gradient of 22℃ per kilometer的作用只能选E,赶脚是这样的