The right answer is B.
Cholera vaccination is only recommended for staff who have to intervene with patients in an epidemic situation. In all other cases, effective prevention is provided by good personal hygiene (washing hands) and food.
It is also important to know that this vaccine does not protect permanently: It protects only about 90% within 6 months, then to 50% within 3 years.
He studies geosphere and biosphere.
The answer is S phase.
If drugs prevent DNA replication which occurs in the S phase. That means that the S phase will be affected by these drugs.
