A、It makes people mentally ill. B、It hinders people’s improvement. C、It gives people too much stress. D、It makes people successf

Now listen to the following recording and answer questions 16 to 19.
Moderator:
    Hello everybody, I am happy to introduce our respectable speaker for today’s lecture, Dr. Lincoln Duncan. Dr. Duncan, professor of psychology at Harvard University, has written numerous articles and books on the topic of enemy for the recent years,(16)he says in his books that everybody should admit having enemies, no matter how humble and generous they are. OK. Let’s welcome, Dr. Duncan.
Dr. Duncan:
    Hello, everyone. First, answer my quick question: have you got an enemy in your life? Most of you may say yes. But you may have misunderstood what I really meant. The enemy we are talking about today is the one inside your heart.
    We are not born with courage, but neither are we born with fear.(17)Maybe some of our fears are brought on by our own experiences, by what someone has told us, by what we’ve read in the papers. Some fears are valid, like walking alone in a bad part of the town at two o’clock in the morning. But once you’ve learned to avoid that situation, you won’t need to live in fear of it.
    Fears, even the most basic ones, can totally destroy our ambitions. Fear can destroy fortunes. Fear can destroy relationships. Fear, if left unchecked, can destroy our lives. Fear is one of the many enemies lurking inside us.
    The second enemy we face is indecision. Indecision is the thief of opportunity and enterprise. It will steal your chances for a better future. Take a sword to this enemy.
    The third enemy inside is doubt.(18)Sure, there’s room for healthy skepticism. You can’t believe everything. But you also can’t let doubt take over. Many people doubt the past, doubt the future, doubt each other, doubt the government, doubt the possibilities and doubt the opportunities. Worst of all, they doubt themselves. I’m telling you, doubt will destroy your life and your chances of success. It will empty both your bank account and your heart. Doubt is an enemy. Go after it. Get rid of it.
    The fourth enemy within is worry. We’ve all got to worry about something. Just don’t let it conquer you. Instead, let it alarm you. Worry can be useful. If you step off the curb in New York City and a taxi is coming, you’ve got to worry. But you can’t let worry loose like a mad dog that would drive you into a small corner. Here’s what you’ve got to do with your worries: drive them into a small corner. Whatever is out to get you, you’ve got to get it. Whatever is pushing on you, you’ve got to push back.
    The fifth interior enemy is over-caution. It is the timid approach to life.(19)Timidity is not a virtue: it’s an illness. If you let it go, it’ll conquer you. Timid people don’t get promoted. They don’t advance and grow and become powerful in the marketplace. You’ve got to avoid over-caution.
    Do battle with the enemy. Do battle with your fears. Build your courage to fight what’s holding you back, what’s keeping you from your goals and dreams. Be courageous in your life and in your pursuit of the things you want and the person you want to become.
    Hope you enjoyed today’s talk. Thank you!
16. What does Dr. Duncan say in his books?
17. Which of the following is not the source of fear according to the passage?
18. What does Dr. Duncan say about healthy skepticism?
19. What influence does timidity have on people according to Dr. Duncan?