[单选题]
A curve of radius 80 m is bol mn +eyl4r:*anked i1dx un80w3 /xluf)ywd +jn2dat $45^{\circ}$. Suppose that an ice storm hits, and the curve is effectively frictionless. What is the safe speed with which to take the curve without either sliding up or down?
A. 9.4 m/s
B. 28 m/s
C. $7.8 \times 10^{2} \; m/s$
D. The curve cannot be taken safely.