The Symbols +, -, and O Are to Be Used

Multiple Choice

The symbols +, -, and o are to be used to show the results of interactions between individuals and groups of individuals in the examples that follow. The symbol + denotes a positive interaction, - denotes a negative interaction, and o denotes where individuals are not affected by interacting. The first symbol refers to the first organism mentioned.
-What interactions exist between mycorrhizae and evergreen tree roots?

A) +/+
B) +/o
C) +/-
D) o/o
E) -/-