关于内暴露标志物，下列叙述错误的是（） A.外源性物质进入人体的可靠依据 B.与外环

     The passengers on the bus watched with sympathy as Susan made her way carefully up the
steps. She paid the driver and then, using her hands to__1__the seats, settled in one of them.
     It had been a year since Susan became blind. As the result of an accident she was suddenly
thrown into a world of __2__. Susan's husband Mark watched her__3__into hopelessness
and he was _4__ to use every possible means to help his wife.
     Finally, Susan felt ready to__5__to her job, but how would she get there? She used to
take the bus, but she was now too __6__to get around the city by herself. Mark__7__to ride
the bus with Susan each morning and evening__8__she could manage it by herself.
     For two weeks, Mark __9__Susan to and from work each day. He taught her how to
rely on her other __10, specifically her hearing, to determine where she was and how to adapt
to her new __11__.
At last, Susan decided that she was ready to try the trip__12. Monday morning arrived.
Before she left, she hugged her husband__13__ , her eyes filled with tears of gratitude(感激).
She said good-bye and, for the first time, they went their __14__ways. Each day went perfectly,
and a wild excitement __15__Susan. She was doing it!
     On Friday morning, Susan took the bus to work__16__. As she was getting off the bus,
the driver said, "Miss, I sure __17__you." Curious, Susan asked the driver __18__.
     "You know, every morning for the __19__ week, a fine-looking gentleman in a military
uniform has been standing across the corner watching you until you enter your office building
safely," the bus driver said.
     Tears of happiness poured down Susan's cheeks. She was so lucky for he had given her
a gift more powerful than __20__ . That is the gift of love that can bring light where there is
darkness.