half +名词或half of+名词作主语时,谓语动词的单、复数形式由所接名词的单复数形式来决定,名词是中心词
例如：Half (of) the girls are foreigners.
Half (of) the fruit was bad.
In 1620,about half(of) the USA was covered by forests.在1620年,美国一半的土地被森林覆盖着.