what's he going to do when he -----(grow)up?我认为应该是GROWS,可怎么江湖上又流传说填原形,

what's he going to do when he -----(grow)up?我认为应该是GROWS,可怎么江湖上又流传说填原形,
what's he going to do when he -----(grow)up?
我认为应该是GROWS,可怎么江湖上又流传说填原形,

what's he going to do when he -----(grow)up?我认为应该是GROWS,可怎么江湖上又流传说填原形,
不是原形.要用第三人称单数grows.
通常助动词（例如do）,情态动词(must, should, ...),和不定式to 后面才跟原形.

grows
这里要填第三人称单数的。因为是he，所以原形不可以

grows