Look at the Following Production Possibilities Table for Smartphones and Tablets

Look at the following production possibilities table for smartphones and tablets. The table shows the maximum combination of smartphones and tablets of corn that can be produced, when all resources are fully employed. Production Possibilities
Good A B C D E

Based on the above information

A) there is no trade-off between smartphones and tablets.
B) the opportunity cost of producing 30 instead of 20 smartphones is 120 tablets.
C) the opportunity cost of producing 40 instead of 30 smartphones is 30 tablets.
D) the opportunity cost of producing 90 instead of 50 tablets is 50 smartphones.