1 . _____(bacterium) reproduce by dividing and making copies of themselves.  (所给词的适当形式填空)

2 . For example , pesticides can damage the land by killing not only harmful _______(bacterium) and insects , but also helpful ones . (所给词的适当形式填空)

3 . Warm milk is the ideal breeding(繁殖) ground for ________(bacterium). (所给词的适当形式填空)