In Multiple Regression Analysis, the Word Linear in the Term $\beta$

In multiple regression analysis, the word linear in the term "general linear model" refers to the fact that

A) $\beta$ ₀, $\beta$ ₁, . . . $\beta$ _p, all have exponents of 0
B) $\beta$ ₀, $\beta$ ₁, . . . $\beta$ _p, all have exponents of 1
C) $\beta$ ₀, $\beta$ ₁, . . . $\beta$ _p, all have exponents of at least 1
D) $\beta$ ₀, $\beta$ ₁, . . . $\beta$ _p, all have exponents of less than 1