The answer is 'he tried to climb the tree'. 'Try' can be used with the infinitive (to climb) or the gerund (climbing) 'Try' with the infinitive means you want to do something but you do not actually succeed in doing it. 'He tried to climb the tree, but he could not.' The infinitive is also used when you are asking someone to do something they may or may not be able to accomplish. 'Try not to wake the baby when you get home.' 'Try' with the gerund means to try or experiment with different methods to see if something works. 'She tried looking for a job in the newspapers and with a recruitment agency but she found nothing.' 'Try' with the gerund is also used when you experiment with something but you do not really like it or want to do it again. 'She tried eating snake soup but didn't really like it.'

tried + infinitive if he ultimately didn't complete the action

He tried to climb the tree, but could not. try to do = you can succeed or fail try doing = you're doing it so you can't fail

Yeah, the answer is A. He tried to climb the tree but he couldn't. Explanation: try to do something: you make an attempt or effort to do something. He tried to climb: He made an attempt, try his best to climb but he couldn't do it. Try + doing something: it means you test something to see if it is good, suitable or not. Hope you could get it.

He tried to climb the tree. Explanation: because you asked, I answered (hope I got it right).