题目

Passing through the Atlanta airport one morning, I caught one of those trains that take     41       to their boarding gates. The trains run      42      all day long. Not many people consider them     43     , but on this Saturday I heard laughter. We had just stopped to    44     passengers, and the doors were closing again. “Here we go! Hold on to me tight!” the father said. The boy, about five years old, made sounds of sheer（纯粹的）    45    . “Look out there!” the father said to his son. “See that pilot? I bet he’s walk下列容器中盛放的物质是纯净物的是A.B.C.D.