The number of integral values of a for which the system of linear equations ` x sin theta -2 y cos theta -az=0`, `x+2y+z=0,-x+y+z=0` may have non-trivial solutions, then
A. at a=2 the given system will have finite solutions for ` theta in R `
B. number of possible integral values of a is 3
C. for a=1 the sytem will have finite solutions
D. for a=3 the sytem will have unique solution