People who are well are likely to be better able to resist disease and to fightdisease when it strikes.
本句的主干是people are likely to be better able to resist disease and to fight disease。 who引导定语从句，修饰people; when引导时间状语从句。
1) I can never resist an ice cream.我一向对冰激凌无法抗拒。
2) They are determined to resist invasion.他们决定抵抗侵略。
Perhaps you will kindly give us a hand when we are in trouble.当我们陷入困境时，可能你会善意地帮我们一把。
Do they possibly wait outside the station?他们可能在车站外面等着吗?
She is potentially our best player, but she needs to practice much harder.她有可能成为我们最好的球员，但她需要加倍训练。
He's late--he's probably stuck in a traffic jam.他迟到了—很可能是遇到了交通拥堵。