15 .what is the main of the passage ?

A. People tend to be optimistic even in crisis.

B. Optimists enjoy life better than pessimists.

C. Being optimistic has both benefits and risks.

D. Optimism is what keeps us going forward.

Questions 16-20 are based on the following passage:

The International Olympic Committee (IOC) has launched an investigation into allegations that its officials in more than 50 countries have been selling London Olympics tickets on the black market for profit. The IOC met at an emergency session on Saturday to look into a pile of evidence uncovered by Britain's Sunday Times newspaper. The paper claims that high-ranking Olympic officials have been selling tickets for the games at hugely inflated prices. The highest priced tickets on the black market were for the men's 100-meter final. The roc has issued a statement saying it takes these allegations very seriously and has immediately taken the first steps to investigate. "

IOC rules forbid national Olympics committees from selling tickets overseas， increasing ticket prices or selling tickets to unauthorized，third-party resellers. Despite this， Sunday Times undercover report posing as illegal ticket sellers say they have recorded evidence of 27 officials selling tickets distributed to 54 countries One of the most serious allegations was against the Greek Olympic Committee president Spyros Capralos. He denies saying he had "pulled strings" with the head of the London Olympics Sebastian Coe even though the paper posted videos of its reporters' negotiations with Capralos on itswebsite. Mr Capralos has so far refused to comment.

16 The IOC is investigating its own officials for _______.

A. running the black market

B. secretly meeting reporters

C. illegally selling tickets

D. criticizing Sunday Times

17. Theword “allegations “(Para.1)”probably means “_______”

A. discussions

B. claims

C. announcements

D. Opinions