He was able to____(ride)a bike when he was 8.

He was able to____(ride)a bike when he was 8.
He was able to____(ride)a bike when he was 8.

He was able to____(ride)a bike when he was 8.
ride

be able to do 能够做……
所以填 ride 原形就行了

ride, 他八岁的时候就会骑自行车了
be able to do sth, 会/能做...