Let non-zero vectors $\boldsymbol{a}, \boldsymbol{b}$ satisfy $|\boldsymbol{a}+\boldsymbol{b}| = |\boldsymbol{a}-\boldsymbol{b}|$, then
A. $\boldsymbol{a} \perp \boldsymbol{b}$
B. $|\boldsymbol{a}| = |\boldsymbol{b}|$
C. $\boldsymbol{a} \parallel \boldsymbol{b}$
D. $|\boldsymbol{a}| > |\boldsymbol{b}|$