This box of apples are sweet.还是This box of apples is sweet.

This box of apples are sweet.还是This box of apples is sweet.

This box of apples is sweet.
该句的意思是：这个苹果盒子是甜的.
很显然该题主语是box,而非apples,它只是用来修饰盒子box的后置定语

This box of apples is sweet
凡有单位名词的,以单位名词为准

This box of apples is sweet.