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. 正确答案是 : 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. 我不理解的是, and at lower cost 在这里的结构, 如果是说deliver a heavier load of instruments into orbit at a lower cost , 是不是可以直接用and ,不加 "," . at lower cost 后面是不是也省略了than ..... 请教各位? | 
