Answer
a) $\exists x(C(x)\land D(x)\land F(x))$
b) $\forall x (C(x)\lor D(x)\lor F(x))$
c) $\exists x(C(x)\land \neg D(x) \land F(x))$
d) $\neg \exists x(C(x)\land D(x)\land F(x))$
e) $\exists xC(x), \exists xD(x), \exists xF(x)$
Work Step by Step
First, we think about whether we want $\forall$ or $\exists$, which we decide based on whether we have a blanket statement, in which case we use $\forall$, or whether we have a statement about one student's pets. Then, we plug in the specific values of C(x), D(x), and F(x), which represent the possession of a cat, dog, or ferret for a student $x$.
a) $\exists x(C(x)\land D(x)\land F(x))$
b) $\forall x (C(x)\lor D(x)\lor F(x))$
c) $\exists x(C(x)\land \neg D(x) \land F(x))$
d) $\neg \exists x(C(x)\land D(x)\land F(x))$
e) $\exists xC(x), \exists xD(x), \exists xF(x)$
