Rank of ATA is less than 2
Rank of ATA is equal to 2
Rank of ATA is greater than 2
Rank of ATA can be any number between 1 and 3
Answer is Right!
Answer is Wrong!
The correct answer is $\boxed{\text{B. Rank of ATA is equal to 2}}$.
Let $A$ be a 4 $\times$ 3 real matrix with rank 2. This means that $A$ has 2 linearly independent columns, and hence $A^T A$ has 2 linearly independent rows. Therefore, the rank of $A^T A$ is 2.
Note that the rank of a matrix is equal to the number of linearly independent rows or columns in the matrix.
Option A is incorrect because the rank of $A^T A$ cannot be less than 2, since $A^T A$ has at least 2 linearly independent rows.
Option C is incorrect because the rank of $A^T A$ cannot be greater than 2, since $A$ has only 3 columns.
Option D is incorrect because the rank of $A^T A$ is a specific number, which is 2 in this case.