Which of the following functions is continuous but not differentiable at x = 1?

Functions:

I.y=3√x-1

II.y={x^2,x≤1
2x,x>1
III. y={x,x≤1
1/x,x>1

I'm not really sure how to do this, but I've been trying and I keep getting

both I and III.. am I wrong?

Me confuseddd