smooth(adj.平坦的,顺利的); stone(n.石头); straight(adj.笔直的) ; thick ; whenever (1) _______ you walk in the hills, you must wear strong shoes and (2) _______socks. The walk may be fairly(adv.相当)(3) ________ at the start because the path is (4) _________, but later it may get difficult. You should also be careful of (5) _________falling from above.