Answer:
What word has kst in the middle, in the beginning, and at the end?
My first keeps time, my second spends time, my whole tells time.
What does a WW1 Trench, A Submarine and a Popular Phone App all have in common?
The more you take, the more you leave behind.
Two in a whole and four in a pair. And six in a trio you see. And eight's a quartet but what you must get. Is the name that fits just one of me?
Black we are and much admired. Many seek us if they are tired. We tire the horse, and comfort man, and turn White when we've fulfilled your plan.