单选题 .  Something kept scratching on the outside of the tent. I wouldn't have thought much about it     21    I hadn't recently seen a ridiculously     22    film on television in which a monster tried to get into its     23    bedroom by scratching on the door with its claw-like hands. A stupid     24    , but it kept coming back,     25    sleep. When a cry rang out across the moor I crawled out to see what it was all about.
    In a small tent this is less easy than it     26    . After     27    yourself from a cocoon-like sleeping-bag, you have to     28    with the zip-fasteners of the tent from a kneeling     29    . Outside all seemed in order. The     30    noise came from clumps of spiky rushes     31    blown by the wind     32    the canvas. The only     33    I have for the eerie cries is that overhead may have passed a(n)     34    flock of stone curlews, birds which make a diabolical noise.
    The moon was the colour of a corpse. Uncomforted, I crept back into the tent. Dawn was pretty dreary, too. Flocks of drifting clouds had settled down low     35    the horizon, jostling each other, uneasily, like sheep undecided what to do next. Hoping fervently they would push off, I paced     36    and walked on, taking the left     37    of the River Tavy, looking for its junction with the tributary that led to Great Kneeset. Nattor Down loomed up where it should have been, but another apparently unmapped hill popped     38    on the opposite side of the torrent, rather spoiling my simple conception of the landscape.
    The going became difficult,     39    a great deal of the stuff they call clitter, the rubble from the outcrops of granite, had fallen down into the gorge. But the compass     40    the heading and I scrambled along as fast as I could in weather that seemed to be worsening. I decided to make for some high place where I could look around and see whether it looked safe to go on.21.