Corrine wrote temperatures in degrees Celsius and the equivalent temperatures in degrees Fahrenheit.

Equivalent Temperatures
Celsius
–10
5
10
20
Fahrenheit
14
41
50
68

Which explains how Corrine could determine if the temperatures vary directly?
Compare the equivalent temperatures as a ratio; if the ratios are equivalent, then the temperatures vary directly.
Draw a graph of the temperatures; if the points form a straight line, then the temperatures vary directly.
Write an equation that converts one temperature to another; if the temperatures satisfy the equation, then they vary directly.
Look for a pattern in the table; if the pattern is consistent, then the temperatures vary directly.