Yes i guess the greased the back axle suspension joints.

*It depends upon the application in which you are using the oil.
Right oil for the right application.

So, the answer should be C that is "ALL SYSTEMS REQUIRE THE SAME AMOUNT OF MAINTENANCE"

[Pl. read below:
Hydraulic fluids are a large group of fluids used as the motive medium in hydraulic machinery. These include of mineral oil, water, and water-based mixtures. The fluids are found in machinery and equipment ranging from brakes, power steering, and transmissions to backhoes, excavators, garbage trucks and industrial shredders.

Base stock may be any of: castor oil, glycol, esters, ethers, mineral oil, organophosphate ester, Chutte and polyalphaolefin, propylene glycol, or silicone. Some of the trade names for hydraulic fluids include Durad, Fyrquel, Houghton-Safe, Hydraunycoil, Lubritherm Enviro-Safe, Pydraul, Quintolubric, Reofos, Reolube, and Skydrol.

Environmentally sensitive applications (e.g. farm tractors and marine dredging) may benefit from using biodegradable hydraulic fluids based upon rapeseed (Canola) vegetable oil when there is the risk of an oil spill from a ruptured oil line. Typically these oils are available as ISO 32, ISO 46, and ISO 68 specification oils. ASTM standards ASTM-D-6006, Guide for Assessing Biodegradability of Hydraulic Fluids and ASTM-D-6046, Standard Classification of Hydraulic Fluids for Environmental Impact are relevant. 2004 prices were about $6/liter in small quantities.

Brake fluid is a subtype of hydraulic fluid with high boiling point and low freezing point.

Hydraulic systems like the ones mentioned above will work efficiently if the hydraulic fluid used has low compressibility.

Fire resistance is a property available with specialized fluids.

Hydraulic fluids can contain a wide range of various chemical compounds; oils, butanol, esters (e.g. phthalates, like DEHP, and adipates, like bis(2-ethylhexyl) adipate), polyalkylene glycols (PAG), phosphate esters (e.g. tributylphosphate), silicones, alkylated aromatic hydrocarbons, polyalphaolefins (PAO) (e.g. polyisobutenes), corrosion inhibitors, etc.

Because industrial hydraulic systems operate at thousands of PSI and temperatures reaching hundreds of degrees Celsius, severe injuries and death can result from component failures and care must always be taken when performing maintenance on hydraulics.

http://www.engineersedge.com/lubrication/water_glycol_hydraulic_fluid.htm
http://en.wikipedia.org/wiki/Hydraulic_oil

A watery mucus?

As said above, the vacuum pump is engine driven and will fail in the event of an engine failure, so unless your gyros use a venturi, they will eventually go out.

The gyros (attitude indicator and DG) will not stop working completely right away. The gyros will still be spinning, but they will begin slowing down. If you turn, the DG and attitude indicator will still indicate a turn, but the DG will precess and eventually stop and the attitude indicator will eventually stop indicating the correct attitude.

In an engine failure in VFR, you should not even be looking at these instruments, so the vacuum failure is really inconsequential. You will learn how to recognize just a vacuum failure, and as mentioned these are far more common. These are also a non-issue when operating VFR, and non a big issue when IFR.