The Internet, as _____ means of communication, has been popular since _____ early 1990s. [ ]

A. a ; the

B. a ; /

C. a ; an

D. the ; an

根据国际商会《跟单信用证统一惯例》的规定，如果信用证上未注明“不可撤销”的字样，该信用证应视为( )。

A．可撤销信用证

B．远期信用证

C．不可撤销信用证

D．由受益人决定可撤销或不可撤销