[单选题]
A box with a mass of M rests on a balance in an elevator thar *gt9.:p9fp bdabesa) 4wb8et isrp.q:t0mpf1xm tg9k 4w l(t u; moving downwards. The p4:x; rl q0p1kwmmf t.t(u9 gtelevator slows with an acceleration of $\frac{g}{4}$.
Which of the following gives the reading of the balance?
A. $\frac{5Mg}{4}$
B. $Mg$
C. $\frac{3Mg}{4}$
D. $\frac{Mg}{2}$
