Which of the Variables Would Probably Be Most Interesting to Researchers

Which of the variables would probably be most interesting to researchers interested in individual differences?

A) Variable A, which is stable over time and has few concurrent associations with other variables
B) Variable B, which has many concurrent associations and changes drastically over short time periods
C) Variable C, which is stable over time and is related to few individual differences over time
D) Variable D, which has many concurrent associations and remains stable over time