Unlike the short flights of the shuttle and earlier spacecraft, which carried sufficient power in fuel cells and batteries, a permanently orbiting space station will have to generate its own electricity.

1. the short flights of the shuttle and earlier spacecraft, which carried sufficient power in fuel cells and batteries
2. the shuttle and earlier spacecraft, with sufficient enough power in fuel cells and batteries for their short flights
3. the short flights of the shuttle and earlier spacecraft, which enabled them to carry sufficient enough power in fuel cells and batteries
4. the shuttle and earlier spacecraft, which were capable of carrying sufficient power in fuel cells and batteries for their short flights
5. the flights of the shuttle and earlier spacecraft, whose shortness allowed them to carry sufficient power in fuel cells and batteries

个人选了Ｂ，可正确答案为Ｄ，请赐教．

if B were the shuttle and earlier spacecraft, with sufficient power in fuel cells and batteries for their short flights, B would be better than D.

Because "sufficient enough power" is redundant, either sufficient power or enough power is good enough.