unresolved constants in DE solution

Why do I have the 2 unresolved constants %k2 and %k1
at %o5 below?  

I can't think of any other initial conditions
beside 'diff(x,t)=0 and x=0 at t=0

Thank you.


'diff(x,t,2) + A*'diff(x,t)^2 + B*'diff(x,t) + D = 0;

ode2(%,x,t);

p;

ic2(%,t=0,x=0,'diff(x,t)=0);
                                               2
                             dx      dx 2     d x
(%o1)                    D + -- B + (--)  A + --- = 0
                             dt      dt         2
                                              dt
(%i2) 
             2
Is  4 A D - B   positive or negative?

                                                        2
                                (t + %k1) sqrt(4 A D - B )
                      2 log(sec(--------------------------)) + t B
                                            2
(%o2)       x = %k2 - --------------------------------------------
                                          2 A