core

这个问题的核心在于如何平衡效率与公平。

The ___core of the issue is how to balance efficiency and fairness.

丢弃了苹果核后，他把它扔进了堆肥箱。

Discarding the apple ___core, he tossed it into the compost bin.

她仔细地切掉了梨坚硬的核。

She carefully cut out the tough ___core of the pear.