[填空题]Up until now, scientists still could not explain how leaves will change colors during the fall.

[填空题]Some scientists explain that touching gives premature babies a better chance to survive because it ______.

[单项选择]He could never be (content) until he could afford to buy that beautiful car.
A. full
B. rich
C. wise
D. happy

[单项选择]Until now the ______ of life is still beyond the knowledge of most common folks: few people know how and in what way the human organs are working and functioning.
A. wheels
B. fate
C. reels
D. parts

[单项选择]It was the first snow of winter. Up until now, I had been able to dress myself for recess(课间休息), but today I would need some help. Miss king, my kindergarten teacher, may still remember this one.
I managed to get into my snow pants, but I struggled with my jacket because it did not fit well. It was a hand-me-down from my brother. Finally it was time to have Miss King help me with my boots. She said, "By the end of winter, you will be able to put on your own boots."
I handed her my boots, and she managed to get the first one into place and then worked the second one on, too.
I said, "They are on the wrong feet". She struggled to get the boots off and tried again. Then I said, "These aren’t my boots, they are my brother’s boots and I hate them!" Somehow, she managed to act as though I was not an annoying little girl. She pushed and shoved, less gently this time and the boots were returned to their proper place on my feet. Seeing the end of her struggle with me, she asked,
A. the pants and jacket
B. the jacket and boots
C. the jacket and hat
D. the gloves