1. face（脸）的英文解释是：the front part of your head, where your eyes, nose, and mouth are，指头部的正面部分，其上有眼睛、鼻子和嘴巴。可见一个人只有一个 face，所指一个人的脸时，总是用单数。如：

The child had a round face. 那孩子有一张圆脸。

His annoyance showed on his face. 他满脸不高兴的样子。

He had a surprised expression on his face. 他脸上露出了惊讶的表情。

2. cheek（面颊，脸颊）的英文解释为：the soft round part of your face below each of your eyes，指每只眼睛下面柔软的圆形部分，可见一个人有两个 cheek（每只眼睛下面一个cheek），也正因为如此，所以它通常是用复数的。如：

Tears ran down my cheeks. 泪水淌下我的双颊。

Her cheeks had a healthy glow. 她面颊健康红润。

The baby has nice plump cheeks. 这婴儿的脸蛋胖乎乎的。

It brought the faint flush to her cheeks. 这使他脸上泛起淡淡的红晕。

当然，若指一边的 cheek 也可以用单数。如：

There is a small mole on her cheek. 她脸颊上有一颗小痣。

She laid her cheek against his. 她把自己的面颊贴 他的脸颊。

A cut on his cheek was still oozing blood. 他脸上的伤口还在渗血。