C.表语从句不能省略that，且能用主谓宾的句子the government predicts'，就不要用抽象名词的主系表government's prediction is……
同B，被动没必要
one thing you should definitely notice in choice c is the wordiness of 'the government's prediction is'. constructions like that, which can easily be replaced by more compact forms ('the government predicts') with no change in meaning, are ALWAYS wrong. (also, you need the word 'that' after 'is'.)
B，被动没必要，且被动的be reduced by sb.离得太远了，有就近修饰calls的歧义！——calls by the Federal Communications Commission's recent telephone rate cuts
the passive voice is indeed a problem, because it's unnecessary. (remember that the passive voice should only be employed when there's a fairly compelling reason to use it.) in choice b especially, there's also an unacceptably long distance between the passive-voice action (will be greatly reduced) and the agent of that action (by the ...).
C选项错在，several improvements in blowing machinery前面的介词是不能省略的。因为，With charcoal's being replaced by coal as the fuel used in the smelting of iron ore中的with是独立主格的with，不是一个普通的介词，而several improvements in blowing machinery是一个纯名词，身前需要一个真正的介词。
as large, integrated companies, such as BethlehemSteel, that 中的as large, integrated companies需理解清楚， large和integrated用作形容词修饰companies，所以large并不是和as一起，as单独使用，表示“因为”。
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C.表语从句不能省略that，且能用主谓宾的句子the government predicts'，就不要用抽象名词的主系表government's prediction is……
同B，被动没必要
one thing you should definitely notice in choice c is the wordiness of 'the government's prediction is'. constructions like that, which can easily be replaced by more compact forms ('the government predicts') with no change in meaning, are ALWAYS wrong. (also, you need the word 'that' after 'is'.)
D 主句缺谓语