______ some teenagers don’t realize is _______ difficult life can be after they get addicted to drugs．

A．What, how

B．That, how

C．What, what a

D．That, what

奠定中国近代铁路网的基本格局是在 [ ]

A、洋务运动时期前

B、戊戌变法前

C、辛亥革命前

D、辛亥革命后