21.What is the 21st word?
举一反三
- “21 Century Cup” English Speaking Competition is sponsored by 21st Century.
- This story happened on __________.( ) A: 2009, Oct.21st B: Oct. 21st, 2009 C: 2009, 21 October D: 21st of October, 2009
- What time would he like to leave？（） A: Tuesday. B: The 20th of December. C: The 21 st of December. D: Next Thursday.
- Questions for video 21) What is the topic of this video clip?
- Assume a non-price discriminating monopolist can sell 20 units of a good for 4.00 each and can sell 21 units of that good for $ 3.85 each. The marginal revenue of the 21st unit is: