4. The story of two babies switched mainly indicates that 　　　.

A. slaves were forced to give up their babies to their masters

B. slaves' babies could pick up slave-holders' way of speaking

C. blacks' social position was shaped by how they were brought up

D. blacks were born with certain features of prejudice

5. What does the underlined word "they" in Paragraph 7 refer to?

A. The attacks. B. Slavery and prejudice.

C. White men. D. The shows.

6. What does the author mainly argue for?

A. Twain had done more than his contemporary writers to attack racism.

B. Twain was an admirable figure comparable to Abraham Lincoln.

C. Twain's works had been banned on unreasonable grounds.

D. Twain's works should be read from a historical point of view.

Ⅱ.任务型阅读

　　It is now mandatory(强制的)for drivers or passengers to wear seat belts while in a car in all states. In addition, it is also mandatory for kids to be in some kind of specialized car seat. Given the strict requirements in other vehicles, why don't buses have seat belts?

　　The main answer, at least for school buses, is that seat belts do not make school buses safer. Overall, traveling on school buses is the safest way to travel-40 times safer than riding in a car-with only a handful of deaths occurring to passengers on school buses every year. The seats on the school bus are placed very close to each other and have high backs that are thickly padded. As a result, in an accident the students would be propelled forward a very short distance into a padded seat back that in a way is like an airbag. In addition, the fact that people sit high off the ground on school buses also makes it safer to travel on them.

While school buses feature high backed seats and elevated seating locations, the same cannot be said of city buses. However, from a practical angle, there's little need to require seat belts on city buses. Although the design of the modern low-floor city bus is less safe than the design of school buses, the fact that city buses rarely travel at speeds greater than 35 miles per hour means that any collision is likely to be small. Also, given that most trips on city buses are short and that