一般情况下，由and连接的两个单数形式的名词作主语时，其后谓语动词用复数形式：
Science and technology seem to be playing a more and more important role in international cooperation.
当 and连接的两个单数名词在意义上指同一人，同一事物，或同一概念，后面一名词没有冠词时，谓语应用单数。
A cart and horse was seen at a distance.
If a law and order is not preserved, neither citizen nor his properity is safe.
1. 但如果后面那个名词前有冠词，谓语动词应该用复数。
The bread and the butter are on sale.
2. and not 连接的两个单数名词，其谓语动词应用单数。
The farmer and not the city deweller is hurt when food prices fall.
