The correct option is A f(x) is strictly increasing function
f(x)=x3+bx2+cx+d(0<b2>c)Ifx→∞,f(x)→∞x→−∞,f(x)→−∞f′(x)=3x2+2bx+cD⇒(2b)2−4×3×c=4b2−12c=4(b2−3c)(0<b2>c)=4(b2−c)−8cNow,D<0So,f(x)hasnotrealroots.f(x)isstrictlyincreasingfunction.hence,optionAiscorrectanswer.