Why can't I use ' after' in the following sentence which imples 40 years should pass before we estalish a colony on mars?
The famous British scientist, Stephen Hawking, belives that there could a colony on Mars in/within/( After?) 40 years. NASA scientists are at present working on models of a space colony, permanent living quarters orbiting the Earth.
After is used in conjunction with a past tense verb He went to school after he ate lunch A colony was built on Mars after 40 years of exploration of the planet . . the action has been completed.
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