Right answer:
B. ni
This sentence stands for negation that is an expression that means no and is used to contradict some or all of the meaning of a positive sentence. So the basic form is when using only the word no. However, there are many other negative words and phrases that you can use to negate a positive statement besides the basic form no. So one of these forms is ni...ni that means neither...nor. Finally:
Isabela: No puedes permitir entrar ni vendedores ni perros callejeros.
