两点测验和()是基因定位所采用的主要方法。
参考答案:三点测验
–A boy was killed by the tiger in the zoo.
–He was believed ______ into the cage while feeding the tiger without permission.
A.to fall
B.to be falling
C.to have fallen
D.having fallen
单轨吊机车“开锅”原因及排除方法?