Answer:
1. by spraying them with insecticide
2. sucking the blood of animals and humans
Step-by-step explanation:
In the first statement, it is said that the tsetse flies can be controlled by sterilizing. The statement form is similar to the first option where the verb of the sentence is is in the same tense and the subject of the sentence comes after the present continuous verb form.
Likewise, in the second sentence the verb tense coincides with the second sentence i.e option B
Hence the correct answers are
1. by spraying them with insecticide
2. sucking the blood of animals and humans