What would be the properties of an ideal astronomical detector? how closely do the actual properties of a ccd approach this ideal?

Ohm's law tells you that i = v/r where v is equivalent voltage and r is equivalent resistance of the circuit
since all circuits have the same voltage, your question is really asking which circuit has the lowest total resistance, since the lower the resistance, the higher the current
circuit a has a resistance of 5 ohms; circuit c is in series so has a resistance of 10 ohms; circuit b is in parallel and therefore has a resistance of 2.5 ohms (review your notes on adding resistances in parallel and series); therefore b has the highest current

It is 5 hope this you out 

Answer a descending mass of air will have its temperature increase because of the pressure exerted on it, because its temperature increases it will also be able to hold more water and feel drier;