We walked down a precipitous slope.

Answer: Option B

Precarious : not securely held or in position; dangerously likely to fall or collapse.
Steep : (of a slope, flight of stairs, or angle) rising or falling sharply; almost perpendicular.
Precise : marked by exactness and accuracy of expression or detail.
Gradual : taking place or progressing slowly or by degrees.
Precipitous : dangerously high or steep.

Synonym of Precipitous is Steep