1. What a challenge I must have been to this young teacher!
    对这位年轻老师来说，教我这样一个学生一定是一件非常困难的工作啊!

2. The rise of acquired immune deficiency syndrome (AIDS) around the earth has represented a major challenge to medical progress both in developed and in less — developed countries.
    全球艾滋病的蔓延无论在发达国家还是在欠发达国家都是对医学进步的重大挑战。

3. Then last year, she decided to challenge Embu's mayor, a veteran politician.
    接着在去年，她决定挑战恩布市市长，一位资深政客。

4. Another kind of challenge faced the Egyptians between 4,000 and 5,000 years ago when they decided to build the first Pyramid.
    四千到五千年之前，埃及人建造第一座金字塔时面临着另外一种挑战。

5. And many of us are interested in the challenge of space.
    我们很多人还对来自太空的挑战深感兴趣。

6. A fixed stare can seem like aggressive behavior if it is a challenge as to who will look away first.
    目不转睛的盯视会被看成是一种攻击性的行为，仿佛双方是在比拼，看谁先把目光移开。

7. "The problem is that to improve balance, you've got to challenge balance, which is always risky," says Mary E. Tinetti of the Yale University School of Medicine,
    "问题是，要提高平衡能力，就得首先挑战平衡。这样做总是有风险。"耶鲁大学医学院的玛丽·E. 蒂内提说。

8. "I challenge that. You didn't do either your grammar or your spelling homework."
    "我有意见，你没做语法作业，也没有做拼写练习。"

9. "The challenge is telling things people already know — and at the same time making it different," the spokesman said.
    这位发言人说："难的是要将人们已熟知的事说得让它听起来不同。"

10. Medical science faces the challenge of conquering the many diseases which still attack human beings.
    医学界面临着征服那些侵害人体的多种疾病的挑战。