生物源性线虫
参考答案：
发育过程中需要中间宿主的线虫，称为生物源性线虫，寄生于组织内的线虫多属此型，如丝虫。
数字460123保留三个有效数字，可写成______．
The students were told to _____ their English before going abroad.
A．give up
B．polish up
C．use up
D．end up
