It still puzzles today’s scientists_____ some mammals produce their young _____others lay eggs to producetheir offspring (后代)[ ]

Einstein was usually his scientific study that he even forgot to eat.

you please have my car ready today—Sure, the damage is not that serious, so it _____beready by 5: 00 pm.

You look upset.What’s the matter？(2011·江苏)—I had my proposal ________ again.

She felt completely ______ during the vacation but now she has to go back to work again