I knew from past experience that hiking the trail would be a c | 📣 Quiz Masters 🇬🇧

I knew from past experience that hiking the trail would be a challenge.

Answer: The unnecessary word(-s) here is(are) < ... past ... > .
TIP: Past means "a time before the present", and experience means "skill or knowledge gained from seeing or doing something".

I knew from past experience that hiking the trail would be a challenge.