Which of the following form(s) a virtual and erect image for all positions of the real object  

For a lens:  $\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$
i.e.,  $\frac{1}{v}=\frac{1}{f}+\frac{1}{u}$
For a concave lens, f and u are negative, i.e., v will always be negative and image will always be virtual 
For a mirror:  $\frac{1}{v}=\frac{1}{f}+\frac{1}{u}$
Here, f is positive and u is negative for a convex mirror. Therefore, v is always positive and image is always virtual.