For a projectile launched horizontally, which of the following best describes the downward component of a projectile's velocity? assume air resistance is negligible. a. the downward component of the projectile's velocity is zero. b. the downward component of the projectile's velocity remains a nonzero constant. c. the downward component of the projectile's velocity continually increases. d. the downward component of the projectile's velocity continually decreases. e. the downward component of the projectile's velocity initially decreases and then increases.