Answer the below question based on the following information:
$\text{A}$ and $\text{B}$ are two sets $\text{(e.g. A =}$ mothers, $\text{B =}$ women). The elements that could belong to both the sets (e.g. women who are mothers) is given by the set $\text{C = A.B.}$ The elements which could belong to either $\text{A}$ or $\text{B}$, or both, is indicated by the set $\text{D = A} \cup \text{B}.$ A set that does not contain any elements is known as a null set, represented by $\phi$ (for example, if none of the women in the set $\text{B}$ is a mother, they $\text{C = A.B}$ is a null set, or $\text{C} = \phi).$
Let $\text{‘V'}$ signify the set of all vertebrates; $\text{‘M'}$ the set of all mammals; $\text{‘D'}$ dogs; $\text{‘F'}$ fish; $\text{‘A'}$ Alsatian and $\text{‘P'},$ a dog named Pluto.
Given that $\text{X = M.D}$ is such that $\text{X = D},$ which of the following is true?
- All dogs are mammals.
- Some dogs are mammals.
- $\text{X} = \phi$
- All mammals are dogs.