What do the betas represent in the multifactor version of the APT?

R$=$RF$+($R$1$RF$)\backslash$beta $1+($R$2$RF$)\backslash$beta $2+($R$3$RF$)\backslash$beta $3+...+($R$$K$$RF$)\backslash$beta K

Multiple choice question.

They represent the portfolio's standard deviation with respect to each factor.

They represent the security$\text{'}$s beta with respect to each factor.

They represent the responsiveness of beta to the risk$-$free rate.