Complex sentence: Three were transported to and left on the moon via the Apollo 15,16, and 17, missions with the fourth rover used for spare parts on the first three following the cancellation of Apollo 18.
Split into simpler sentences: Three were transported to and left on the moon via the Apollo 15,16, and 17, missions. The final rover was used for spare parts for Apollo 15,16, and 17, following the cancellation of Apollo 18.