It was the last day of the final exam in a college. On the steps of building, a group of engineering students were waiting for the last exam. On their faces was confidence（自信的）. 
They knew the exam would be easy. The professor (a teacher at a college) had said they could bring any books or notes during the test.
Right after they came into the classroom. The professor handed out the papers. There were only five questions on it.
Three hours passed. Then the professor began to collect the papers. The students no longer looked confident. On their faces was nervous expression（表情）. The professor watched the worried faces before him, and then asked, “How many of you have finished all five questions?” No hand was raised. “How many of you have answered four?” Still no hands. “Three? Two?” The students moved restlessly in their seats. “One, then? Certainly somebody has finished one.” But the class kept silent. The professor said, “That is exactly what I expected. I just want to make you know clearly that even though you have completed four years of engineering. There are still many things about the subject you don’t know. These questions you could not answer are common in everyday practice.” Then, smiling, he added, “You will all pass this course, your education has just begun.”
The years have obscured the name of this professor, but not the lesson he taught.
Why did the students think the exam was easy at first?

A．Because it was their last exam in the college.

B．Because they knew there were only five questions.

C．Because they thought they were clever and talented.

D．Because they were allowed to bring any books and notes during the text.

What does the underlined word “obscured” mean in the last paragraph?

A．模糊

B．回忆

C．提醒

D．改变

. What’s the best title for the article?

A．Some Confident Students.	B．An Engineering Exam.
C．An Interesting Professor.	D．An Unforgettable Lesson.