椎管内肿瘤最常见的发病部位是（）
A.颈段
B.胸段
C.腰段
D.骶段
E.尾段
参考答案：B
解析：发病跟椎管长度有关，胸段最长，故多发。
The achievements of the greatest minds in science could never have been reached if it had not been for the patient and accurate work of hundreds of other people.
A．has it not been
B．if it had been
C．if hasn't been
D．had it not been
基因型为AABB的个体和aabb的个体杂交，F2代中，基因型与亲本相同的个体占总数的多少？重组性状类型个体数约占总数多少？纯合体占总数多少（）
A.1／8、3／8、1／4
B.3／8、1／8、9／16
C.5／8、1／4、3／16
D.1／4、3／16、1／16
