Answer=C

According to the question, 

• Initial velocity (v_i) = 5 m/s
• Final velocity (v_f) = 25 m/s
• Time (t) = 20 s

Acceleration is calculated as 

$\overrightarrow{a}=\frac{V_{f}-V_{i}}{t}$

$\overrightarrow{a}=\frac{25-5}{20}$

∴ a = 1 m/s²

Thus, the acceleration of the truck is 1 m/s².