Question about u and h and Its Differential Changes for Ideal Gases

Hello

1. I was wondering why internal energy is usually expressed as a function of temperature and specific volume and enthalpy a function of temperature and pressure (ie why is u(T,v) and h(T,p)) and some other set of two properties?

2. For du = [itex]\frac{∂u}{∂T}[/itex]dT + [itex]\frac{∂u}{∂v}[/itex]dv and dh = [itex]\frac{∂h}{∂T}[/itex]dT + [itex]\frac{∂h}{∂p}[/itex]dp, why are the [itex]\frac{∂u}{∂v}[/itex] and [itex]\frac{∂h}{∂p}[/itex] terms zero for ideal gases only?

3. Why are the specific heats for ideal gases a function of temperature only? For real gases does this become cv(T,v) and cp(T,p)?

Thanks very much