subject
Frequency is a noun.
The word inventions is a noun. It is the plural form of invention.
Depending on whether the air conditioner is a "central operating unit" or if it is a "stand alone unit". The stand alone is an equipment purchase whereas a "central" is now part of the building.
Accessory - It is a necessary things need to work equipment properly or perfectly.Simple example we purchase one pen, it should with pen cap.Think, with out cap off-course we can write.But it is not a perfect pen.So pen cap is an accessory coming with pen. Spare parts- It is some extra part coming with equipment to future use. Example: Pen refill
part of speech
The part of speech for this particular word is a noun.
adverb
what part of speech is beneath
The part of speech for "answer" is a noun.
The part of speech for "explicit" is an adjective.
The part of speech for "unfamiliar" is an adjective.
The part of speech for "indefinite" is an adjective.
The part of speech for "lecturer" is a noun.
The part of speech for "breezy" is an adjective.
The part of speech for "buried" is a verb.
The part of speech for "rapid" is an adjective.