A curve with equation of the form `y=a x^4+b x^3+c x+d` has zero gradient at the point `(0,1)` and also touches the `x-` axis at the point `(-1,0)` then the value of `x` for which the curve has a negative gradient are: a.`xgeq-1` b. `x<1` c. `x<-1` d. `-1lt=xlt=1`