[单选题]
A beam of electrons rkqk7x(s; )z(d/j 04fykhugf p v3l t.ly4 r 8;vg/wadenters a uniform electric field, as shown.
What effect does this field have on the horizontal and vertical components of the electrons' velocity?
A. Horizontal velocity is Increases ; Vertical velocity is Stays the same
B. Horizontal velocity is Decreases ; Vertical velocity is Stays the same
C. Horizontal velocity is Stays the same ; Vertical velocity is Increases
D. Horizontal velocity is Stays the same ; Vertical velocity is Decreases