They __________ all over the country. So they plan __________ some other countries.[ ]

A. have traveled; visit

B. traveled; to visit

C. traveled; visiting

D. have traveled; to visit

下列氨基酸中能转化生成儿茶酚胺的是

A．天冬氨酸

B．色氨酸

C．酪氨酸

D．丙氨酸

E．蛋氨酸