Which of the following indicates a fairly strong relationship between x and y?

Researching a bit I found the rest of your question ...

Which of the following indicates a fairly strong relationship between X and Y?

a. R2=0.9

b. The p-value for the null hypothesis?1=0 is 0.0001

c. The t-statistic for the null hypothesis?1=0 is 30

And the correct answer is a)

R2 (R squared), known as the coefficient of determination, allows us to estimate the quality of a certain model. More specifically, how well data fits the model. This translates in a strong relationship between X and Y.