For Science Physics, you just need to the I-V graphs of ohmic conductor e.g fixed resistor and non-ohmic conductor e.g. filament bulb/lamp. For Pure Physics, all the 4 components are needed.

As the reference height is at B, so above that reference height is considered positive, and below the reference height it is considered negative. Hence the height-time graph is as such. Consider a vertical oscillating object, similar to the simple pendulum, the middle is the fastest.