As you brake your bicycle, your speed changes from $20\frac{m}{s}1010\frac{m}{s}$ in $5$ seconds. What is your acceleration?

A$)-10\frac{m}{s^2}$

B$)2\frac{m}{s^2}$

C$)10\frac{m}{s^2}$

D$)-2\frac{m}{s^2}$