Correct Answer - a,b,cd,
since `veca, vecb and veca xx vecb,` are non- coplanar,
`vecr=xveca + yvecb+z(vecaxxvecb)`
`vecr xx vecb = veca`
` Rightarrow xvecaxx vecb + z {(veca.vecb)vecb - (vecb .vecb) veca}= veca`
`- (1+z|vecb|^(2))veca + x vecaxx vecb=0`
`x = 0 and z= 1/(|vecb|^(2))`
Thus, `vecr = y vecb - (vecaxx vecb)/ (|vecb|^(2)) ` where y is the parameter.