骨质破坏的基本X线表现是（）
A.骨密度减低
B.骨小梁模糊
C.骨小梁变细
D.骨结构紊乱
E.骨结构局部消失
参考答案：D
目前已知的最强的致泻毒素是（）
A.产气荚膜梭菌肠毒素
B.霍乱肠毒素
C.志贺肠毒素
D.金黄色葡萄球菌肠毒素
E.产毒大肠埃希菌肠毒素
What benefit is a weather bulletin to a mariner（）.
A.It provides a legal reason to cancel a projected voyage
B.It allows the mariner to make long term weather forecasts
C.It is of little benefit since the weather changes frequently and rapidly
D.It gives the mariner time to prepare for weather changes
