Select all solutions of $9 u_t = u_{xx}$. There may be more than one correct answer.

A. $u = e^{3 x - t}$

B. $u = e^{3 x + t} + 3 t + 6$

C. $u = 3 e^{x+t}$

D. $u = e^{3 x + t + 6}$

E. $u = e^{6 x - 9 t}$

F. $u = 3 e^{3 x + t}$

G. $u = e^{3 x + t} + 3 x + 6$

H. $u = 0$

I. $u = e^{6 x + t }$

J. $u = e^{3 x + t}$

K. None of the above