请教OG179

179. During the early years of European settlement on a continent that was viewed as "wilderness" by the newcomers. Native Americans, intimately knowing the ecology of the land. were a help in the rescuing of many Pilgrims and pioneers from hardship, or even death.

(A)  Native Americans, intimately knowing the ecology of the land, were a help in the rescuing of

(B)  Native Americans knew the ecology and the land intimately and this enabled them to help in the rescue of

(C)  Native Americans, with their intimate knowledge of the ecology of the land, helped to rescue

(D)  having intimate knowledge of the ecology of the land. Native Americans helped the rescue of

(E)   knowing intimately the ecology of the land, Native Americans helped to rescue

Choice A suffers from the wordy and indirect expression were a help in the rescuing of. B creates an awkward, redundant, fused sentence in which the first clause has to be repeated in the vague this of the second clause; further­more, the comma required before and in larger compound D and E are confusingly worded because they begin with present participles (having and knowing) that appear at first to refer to the immediately preceding noun, newcomers, rather than to Native Ameri­cans. D also has the wordy and unidiomatic helped the rescue of. Clear, direct, and economical, choice C is best.

further­more, the comma required before and in larger compound

对于这个语法点不清楚,有没有人点经一下.

用and连接两独立句需要用" , "分隔

谢谢你,现在明白了