据美国驻华大使馆副领事史建邦介绍，此前这类签证的有效期为3个月；签证有效期延长为一年后，
O B-government I-government I-government I-government I-government I-government I-government B-position I-position I-position B-name I-name I-name O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O