A stock having a beta of $2$ means;

a$.$ that the stock is twice as responsive to a change in market return

b$.$ All options are correct

C$.$ that if the stock's return has gone up by $2\%,$ it implies a rise of $1\%$ in the market return

d$.$ that if the market return goes down by $1\%,$ the stock's return will go down by $2\%$