Protons Are Being Accelerated in a Particle Accelerator $\sqrt { 2 }$

Protons are being accelerated in a particle accelerator. When the speed of the protons is doubled, their de Broglie wavelength will

A) increase by a factor of 4.
B) increase by a factor of 2.
C) decrease by a factor of 2.
D) increase by a factor of $\sqrt { 2 }$ .
E) decrease by a factor of $\sqrt { 2 }$ .