听力原文： In some countries certain kinds of insurance are compulsory. In others, most kinds are practically unknown. In addition, the cost of insurance and the type of coverage provided vary widely from country to country. But the basic principle of insurance remains the same, that is, to share the possible risk. Is it wise to spend money on insurance even though a claim may never be made? Is keeping a spare tire in the car a wasted investment, even if the tire is never needed? The sense of security to the car driver may make the expense of the extra tire worthwhile. While financial compensation cannot make up for certain losses, it may compensate for other losses. Much of the insurance bought by individuals falls into the categories of property, health, disability and life insurance. Property insurance is to insure against the loss of property — home, business, cars, or other possessions. It is the most common form. of risk management. Health insurance pays some medical expenses or may pay for only certain medical care. In many places workers may receive insurance as a condition of their employment. Disability insurance provides some income if a person is injured and cannot work. Life insurance provides financial assistance to a persons dependents in the case of his or her death. Such insurance has enabled many families to pay off outstanding debts and carry on their routine of life after the injury or the death of their main breadwinner. Questions 16 to 18 are based on the passage you have just heard. 16. What is the basic principle of insurance? 17. Why does the speaker mention the spare tire? 18. What kinds of insurance are mentioned in this talk?17．