question:  Why was the fuel drained out of Hennessy's ship's tank?
context: They were something more—and something less—they were, in short, humanity's hopes for survival! [Transcriber's Note: This etext was produced from Worlds of If Science Fiction, September 1961. She seemed to be restless to end her fool's errand here, two hundred light years from the waiting hordes on Earth. Captain Gwayne cursed and rolled over, reaching for his boots. Earth couldn't turn out enough starmen in the schools, so promising kids were being shipped out for training as cadets on their twelfth birthday. The two he'd drawn, Kaufman and Pinelli, seemed to be totally devoid of any sense of caution. The blobs hadn't seemed dangerous, and the local animals were apparently all herbivorous and harmless. But something had happened to the exploration party fifteen years back, and to the more recent ship under Hennessy that was sent to check up. The Sol-type sun must be rising, since there was a dim light. Even the deep gorge where they'd found Hennessy's carefully buried ship was completely hidden by the fog. Earth had ordered him to detour here, after leaving his load of deep-sleep stored colonists on Official World 71, to check on any sign of Hennessy. If there was no sign in another day or so of what had happened to the men who'd deserted their ship and its equipment, he'd have to report back. One seemed to be almost eight feet tall, leading the others directly toward the spacesuited cadets. One, at the front, was stuttering into life, and Gwayne dashed for it as the exit port slid back. At a gesture, the jeep rolled down the ramp, grinding its gears into second as it picked up speed. The creatures dived downward into lower ground, beginning to disappear into the mists. Then it cleared to show the mob of creatures doubling back on their own trail to confuse the pursuers. A spear crunched against the windshield from behind, and Gwayne caught it before it could foul the steering wheel.
output:  Hennessy drained it so they couldn't leave
options:  Gwayne doesn't know  Hennessy drained it so they couldn't leave  it was destroyed by creatures from the planet  the blobs used it for energy