Do you know the difficulty he has ---what eco-travel means?

Do you know the difficulty he has ___what eco-travel means?1.Do you know the difficulty he has ___what eco-travel means?A.understand B.understood C.to understand D.understanding 2.____ not to miss the fkight at 15:00,the manager set out for the airportin a hurry.A.Remiding B.Reminded C.To remind D Having reminded 3.And ___ he was in front of Xiaoming A.the following B.the next moment C.for a moment D.just a moment