1） 語法形式上要壹致，即單復數形式與謂語要壹致。
2） 意義上要壹致，即主語意義上的單復數要與謂語的單復數形式壹致。
3） 就近原則，即謂語動詞的單復形式取決於最靠近它的詞語，
壹般來說，不可數名詞用動詞單數，可數名詞復數用動詞復數。
There is much water in the thermos.
但當不可數名詞前有表示數量的復數名詞時，謂語動詞用復數形式。
e.g. Ten thousand tons of coal were produced last year.
Large quantities of water are needed.
In western countries, mountains of rubbish are thrown away each day.
1 並列結構作主語時謂語用復數
Reading and writing are very important.
註意： 當主語由and連結時，如果它表示壹個單壹的概念，即指同壹人或同壹物時，謂語動詞用單數，and 此時連接的兩個詞前只有壹個冠詞。
The iron and steel industry is very important to our life.