OG这题选项中，这个成分怎么说？

frankzhiwei

103. The development of a new jumbo rocket that isexpected to carry the United States into its next phase of space exploration will be able to delivera heavier load of instruments into orbit than thespace 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D最后，comma之后的“and at a lower cost”，不是逗号后有个and就加句子了吗，可是这个是句子吗？？？

请大家解疑~感谢~

frankzhiwei

有高人能解解吗！！？