3. Given $A(3,7), B(5,2)$, after translating $\overrightarrow{A B}$ by the vector $\boldsymbol{a}=(1,2)$, the coordinates of the resulting vector are
A. $(1,-7)$
B. $(2,-5)$
C. $(10,4)$
D. $(3,-3)$
3. $\mathrm{B}$ Hint: $\overrightarrow{A B}=(2,-5)$, coordinates remain unchanged after translation.