\rbqquest{We will develop a theory of  linear equations, complete with an algorithm for 
solving them. It's important to recognize them when you see them.\\

Which of the following are linear ODE's?\\
1. $\dot{x} + x^2 = t$\\
2. $\dot{x} = (t^2+1)(x-1)$\\
3. $\dot{x} + x = t^2$\\
}

\rbqchoice{
a) None\\
b) (1) only\\
c) (2) only\\
d) (3) only\\
e) All\\
f) All but (1)\\
g) All but (2)\\
h) All but (3)\\
}

\rbqans{Equations (2) and (3) are linear; (1) is not: the correct answer is (f).}