Indoor cats and outdoor cats are the compound subject (not including the and), and require is the verb.
A subject can be compound or singular. If it is compound, then both are the subject. Example:John and Jeff rode their bikes.
compound subject
A compound subject is a sentance with two or more subjects.
Tony and I went to the movies. Tony and I is the compound subject.
a compound subject is two or more subjects joined by a conjuction
The subject isn't compound -- Kate is the subject.Wrote and edited is the compound predicate.
Clyde Ormond has written: 'Hunting In The Northwest' 'Bear!' -- subject(s): Bear hunting 'Complete book of outdoor lore' -- subject(s): Natural history, Outdoor life, Outdoor books 'Complete book of hunting' -- subject(s): Hunting
Some compound subject pronouns are someone, anyone, everyone, and whoever.
first of all your sentence is incorect! it would be "What is "a" compound subject"anyways a compound subject is when you have two subjects like in this sentence-Dave and Bill went to the movies together to see 2012.Dave and Bill would be the compound subject.
Richard L. Bury has written: 'Thesaurus of outdoor recreation terms' -- subject(s): Outdoor recreation, Subject headings, Terminology
The compound verb "were flying" is intransitive; it does not require any direct object to complete its meaning, but instead describes an independent characteristic of the subject of a clause in which it occurs.
Indoor pool use less chlorine due to the fact that they are not subject to sunlight. Sunlight is the biggest killer of chlorine in pools. That is why you will use more chlorine in an outdoor pool in June and July because those are the months with the most sunlight. The other factor to take into consideration is bather load, whether an indoor or an outdoor pool.