Which of the following is the most frequently used parameter when comparing two economies?

In the short run

a. new firms may enter an industry. b. existing firms may change the quantity they are supplying. c. price and quantity supplied are absolutely fixed. d. quantity supplied is absolutely fixed.

Which of the following ideas is the most plausible?

a. Tax revenue is more likely to increase when a low tax rate is increased than when a high tax rate is increased. b. Tax revenue is less likely to increase when a low tax rate is increased than when a high tax rate is increased. c. Tax revenue is likely to increase by the same amount when a low tax rate is increased and when a high tax rate is increased. d. Decreasing a tax rate can never increase tax revenue.