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

Two lamps of luminous intensity of $8 \, Cd$ and $32 \, Cd$ respectively are lying at a distance of $1.2 \, m$ from each other. Where should a screen be placed between the two lamps such that its two faces are equally illuminated due to the two sources?

For a candle of $40$ power,the exposure time required for a photographic print at a distance of $0.6 \, m$ is $20 \, s$. What will be the exposure time required for the same print at a distance of $1.2 \, m$ using a candle of $20$ power?

In the figure shown,consider the first reflection at the plane mirror and the second at the convex mirror. $AB$ is the object.

Which of the following statements is correct?

Two blocks each of mass $m$ lie on a smooth table. They are attached to two other masses as shown in the figure. The pulleys and strings are light. An object $O$ is kept at rest on the table. The sides $AB$ and $CD$ of the two blocks are made reflecting. The acceleration of the two images formed in those two reflecting surfaces with respect to each other is: