Koalos sleep __the day,but ___night they get up and eats leaves.

问题描述:

Koalos sleep __the day,but ___night they get up and eats leaves.

Koalas sleep( during) the day,but (at ) night they get up and eats leaves.为什么during the day 在白天 at night在晚上 两个都是固定的表示时间的短语