I find ________ difficult to remember everything, though I’m still young.

If you take this new type of train to Xi’an, it will _________ you only two hours to get there.

I hope to have a job like ________ in the future, Dad．―Good, only if you ________ hard from now on．

There are four ________ students in our school.

People _________ rivers for transportation since the beginning of history.