question:  What clue did the water tanks and tubing give Jery?
context: MASTER SPY OF THE RED PLANET Jery Delvin had a most unusual talent. So when the Chief of World Security told him that he had been selected as the answer to the Solar System's greatest mystery, Jery assumed that it was because of his mental agility. But when he got to Mars to find out why fifteen boys had vanished from a spaceship in mid-space, he found out that even his quick mind needed time to pierce the maze of out-of-this-world double-dealing. For Jery had become a walking bomb, and when he set himself off, it would be the end of the whole puzzle of THE SECRET MARTIANS—with Jery as the first to go! Oddly enough, it worked out, and he now does nothing else. He says, "I'd like to say I do this for fulfillment, or for cash, or because it's my destiny; however, the real reason (same as that expressed by Jean Kerr) is that this kind of stay-at-home self-employment lets me sleep late in the morning." I couldn't find anything really incriminating, unless maybe it was that hair dye that unexpectedly turned bright green after six weeks in the hair, but that was the lab's fault, not mine. "Jery Delvin?" said the one on my left, a note of no-funny-business in his brusque baritone. Yes," I said, some terrified portion of my mind waiting masochistically for them to draw their collapsers and reduce me to a heap of hot protons. They had a car waiting at the curb downstairs, in the No Parking zone. Because the speaker was Philip Baxter, Chief of Interplanetary Security, second only to the World President in power, and not even that in matters of security. "Jery Delvin," he read, musingly and dispassionately.
output:  An idea of how and when the boys went missing - probably during the night
options:  An idea of how and when the boys went missing - probably during the night  An idea of how much water was used during the trip  An idea of how and when the boys went missing - probably via the tanks  An idea as to whether or not the other man was lying