A．sunB．grasshopperC．flyD．tractorAll of the following fa……

High in a smooth ocean of sky floated a dazzling, majestic sun. Fragments of powdery cloud, like spray flung from a wave crest, sprinkled the radiant, lake-blue heaven.
Relaxed on a bundle of hay in a comer of a meadow bathed in sunlight, Paul lay dreaming. A gentle breeze was stirring the surrounding hedges; bees moved, humming thoughtfully, from scarlet poppy to purple thistle; a distant lark, invisible in blue light, was flooding the vast realm of the sky with glorious song, as the sun was flooding the earth with brilliance. Beyond the hedge a brook tinkled over softlyglowing pebbles. Butterflies hovered above nodding clover. An ant was busily exploring the uncharted territory of Paul’s suntanned wrist. A grasshopper skidded briskly over his ankle. And the blazing sun was steadily scorching his fair freckled face to bright lobster red. Neither sun, nor grasshopper, nor ant, however, was able to arouse him.
Not even when a fly started crawling over his face did he open his eyes. For Paul was a thousand miles away, in a world of eternal snow and ice. Across the towering mountain range, a bitter gale was screaming furiously as with one hand he gripped a projecting knob of rock while with his axe he hacked out the next narrow foothold in the rock. As their infallible guide, he was leading his gallant party of climbers up a treacherous, vertical wall of rock towards the lofty peak above, hitherto unconquered by man. A single slip, however trivial, would probably result in death for all of them. To his right he could glimpse the furrowed glacier sweeping towards the valley, but he was far too absorbed in his task to appreciate fully the scene around or even to be aware of a view of almost unearthly beauty. A sudden gust of wind nearly tore him from the ledge where he was perched. Gradually he raised his foot, tested the new foothold on the sheer rock wall, transferred his weight, and signaled to the climbers below.
Not until a tractor started working in the next field did he become conscious of his far from icy surroundings. He sat up, wiped his forehead with his handkerchief, glanced at his watch and sighed in resignation. He had a headache through sleeping in the hot sun, a pain in his shoulder from carrying his rucksack; his legs felt stiff and his feet ached. With no enthusiasm whatever he pulled the bulging rucksack over his shoulders and drew a large-scale map from his pocket. At the far end of the meadow two slates in the wall, which at this point replaced the hedge, indicated a stile, and beyond he could faintly see a thin thread of path which dwindled and finally disappeared as it climbed the steep slope of the down, quivering in the glare of the sun. The whole of Nature seemed to be luxuriating in warmth, sunshine and peace. Wherever he looked, leaves on twigs, grass blades, flower petals, all were sparkling in sunlight.
Fifteen miles off, over the ridge, across a broad valley and then over a higher, even steeper range of hills lay the youth hostel: supper, company, a cool dip in the river. With a momentary intense longing for ice-axe, blizzard, glacier and heroic exploit (none of which was at all familiar to him), Paul strode off unwillingly to less dramatic but equally heroic achievement in the tropical heat of an English sun.
All of the following failed to wake Paul up EXCEPT the ______.

A．sun
B．grasshopper
C．fly
D．tractor