[求助]OG11th 103,烦恼！！ - ChaseDream

103. The development of a new jumbo rocket that is expected to carry the United States into its next phase of space exploration will be able to deliver a heavier load of instruments into orbit than the space shuttle and at a lower cost.

(A) The development of a new jumbo rocket that is expected to carry the United States into its next phase of space exploration will be able to deliver a heavier load of instruments into orbit than the space shuttle and at a lower cost.

(B) The development of a new jumbo rocket is expected to carry the United States into its next phase of space exploration and be able to deliver a heavier load of instruments into orbit at a lower cost than the space shuttle.

(C) The new development of a jumbo rocket, which is expected to carry the United States into its next phase of space exploration, will be able to deliver a heavier load of instruments into orbit at a lower cost than the space shuttle.

(D) A newly developed jumbo rocket, which is expected to carry the United States into its next phase of space exploration, will be able to deliver a heavier load of instruments into orbit than the space shuttle can, and at a lower cost.

(E) A newly developed jumbo rocket, which is expected to carry the United States into its next phase of space exploration, will be able to deliver a heavier load of instruments into orbit than the space shuttle and to cost less.

答案是D。答案怎么选出来的我已经知道了，只是对D向中的“逗号+and at a lower cost”还十分不解。

1. at a lower cost到底在句中作的什么成分啊？

2.从句意上来看，at lower cost 和a heavier load平行，可是前者是介宾短语，后者是名词，两者可以平行吗？

3.即使两者可以平行，前面的逗号+and是怎么回事啊，按理不应该有逗号啊。

请NN们救急啊！！