Which statements are correct?(A) ∃ f:[0,1]→ℝ discontinuous everywhere with |f| continuous everywhere(B) F=f·g, f diff at x=a, f(a)=0, g continuous at x=a ⟹ F diff at x=a(C) Rf'(a)=2, Lf'(a)=3 ⟹ f non-diff at x=a but always continuous(D) f(a) and f(b) have opposite signs ⟹ ∃ solution of f(x)=0 in (a,b) if f continuous on [a,b]