C

Suppose we want to paint a cube so that there remains an unpainted stripe along all the edges on each face. The width of the stripe should be $1\mathrm{cm}$. The producer gives the paint consumption $100\mathrm{ml}/1{\mathrm{m}}^2$. From the following functions choose the one that describes the dependence of the paint consumption $V$ on the length of the cube edge $a$. The paint consumption $V$ is given in millilitres and the length of the cube edge $a$ is given in meters.

Trains run between the towns $M$ and $N$ in both directions. The lines in the distance-time diagram correspond to the uniform movements of trains $A$, $B$, $C$ and $D$ between the towns. Find out which of the trains is the fastest. $$$$ Note: The distance-time diagram as seen in the picture is a graphical representation of trains operating schedule for a certain rout (or routs). Connections are displayed as broken-lines or line segments in rectangular coordinate system, where horizontal is the time axis with the time during an operating day and vertical is the distance axis with distances of the traffic nodes (e.g. railroad stations, cities) from one chosen reference node (in our case the town $N$). Connections in one direction (from $N$ to $M$) are displayed by the lines skewed to the right (trains $B$ and $C$) and back-connections in other direction (from $M$ to $N$) are displayed by the lines skewed to the left (trains $A$ and $D$).

There are graphs of three quadratic functions in the picture. Choose the formula which corresponds to all three functions graphed in the picture. Suppose that $a\in {\mathbb{R}}^{+}$.