Need help multiple choice please

1. Someone who owns stock in a drug company that suddenly and unexpectedly reveals it has found an effective vaccine against AIDS will make a profit on the stock a. at once. b. only if she hangs on to the stock for a number of years. c. only if she sells the stock. d. only when the dividends actually start to increase. 2. Cooperation among different people I economic life can occur a. even if most people know nothing about one another. b. only if at least 10% of the people know one another personally. c. only if the majority of people know one another personally. d. only if everybody knows one another personally. 3. Sunk costs are irrelevant to economic decisions because a. they are merely opportunity costs rather than monetary expenditures. b. they cannot affect a firm's net revenue. c. they do not appear on financial statements. d. they represent no opportunity for choice. 4. How long is it worthwhile to continue searching for a $20 bill that you lost if you value your time at $5 an hour? a. About 2 hours if there is a fifty percent chance of finding it. b. About 4 hours, regardless of the probability of finding it. c. Only so long as you expect to find it within the next four hours, which could mean far more than four hours of searching. d. You cannot make a rational decision without first knowing whether you will find it. e. You should not search at all because the lost bill is a sunk cost