The volatility of Home Depot share prices is $35\%$ and that of General Motors shares is $17\mathrm{.}5\%.$ When I hold both stocks in my portfolio and the stocks returns have a correlation of$1,$ the overall volatility of returns of the portfolio is$\_\_\_\_\_\_\_\_.$

I know a correlation of $1$ means they both do the same thing...

A Unchanged at $35\%$

B Equal to $17\mathrm{.}5\%$

C More than $17\mathrm{.}5\%$

D less than $35\%$