D
The term “multitasking” originally referred to a computer’s ability to carry out several tasks at one time. For many people, multitasking has become a way of life and even a key to success. In fact, some excellent mental aerobic exercises (大脑训练) involve engaging the brain in two or more challenging activities at a time. Although checking e-mail while talking on a phone and reading the newspaper may be second nature for some people, many times multitasking can make us less productive, rather than more. And studies show that too much multitasking can lead to increased stress, anxiety and memory loss.
In order to multitask, the brain uses an area known as the prefrontal cortex (前额叶脑皮层). Brian scans of volunteers performing multiple tasks together show that as they shift from task to task, this front part of the brain actually takes a moment of rest between tasks. You may have experienced a prefrontal cortex “moment of rest” yourself if you’ve ever dialed (拨电话) a phone number and suddenly forgotten who you dialed when the line is answered. What probably occurred is that between the dialing and the answering, your mind shifted to anther thought or task, and then took that “moment” to come back. Research has also shown that for many volunteers, job efficiency (效率) declines while multitasking, as compared to when they perform only one task at a time.
Multitasking is easiest when at least one of the tasks is habitual, or requires little thought. Most people don’t find it difficult to eat and read the newspaper at the same time. However, when two or more attention-requiring tasks are attempted at one time, people sometimes make mistakes.
We often don’t remember things as well when we’re trying to manage several details at the same time. Without mental focus, we may not pay enough attention to new information coming in, so it never makes it into our memory stores. That is one of the main reasons we forget people’s names---even sometimes right after they have introduced themselves. Multitasking can also affect our relationships. If someone checks their e-mail while on the phone with a friend, they may come off as absent-minded or disinterested. It can also cause that person to miss or overlook key information being passed on to them.
68. Why are some mental aerobic exercises designed to engage people in multitasking?
A. To make them more productive.        B. To reduce their stress and anxiety.
C. To develop their communication skills.  D. To help them perform daily tasks more easily.    
69. According to Paragraph 2, why may a person suddenly forget who has called?
A. He may leave his prefrontal cortex temporarily damaged.
B. He is probably interrupted by another task.
C. He is probably not very familiar with the person he has called.
D. He may need a rest between dialing and speaking.
70. People tend to make mistake when ____.
A. they perform several challenging tasks at a time.
B. new messages are processed one after another
C. their relationships with others are affected
D. the tasks require little thought
71. What is the main idea of the passage?
A. Multitasking has become a way of life.  
B. Multitasking often leads to efficiency decline.
C. Multitasking exercises need to be improved.
D. Multitasking enables people to remember things better.