美国密执安湖沙丘上的群落演替为 ( )
A．原生演替
B．次生演替
C．周期性演替
D．异养性演替
参考答案：A
At the science museum，the students from Sunshine Middle School get to know__________.
A．what is the spaceship like
B．what the spaceship looks like
C．how the spaceship looks 1ike
D．how does the spaceship 1ook like
对梅毒性心脏病的定性诊断最有价值的是（）
A.升主动脉壁的线状钙化
B.主动脉瘤呈线状或弧形钙化
C.主动脉弓部中度扩张
D.左心室增大
E.动脉瘤外形为局限性囊状或梭状阴影
