Some of you need to memorize the list of prepositions:
about above across after against among around at before behind below beside between by down during except for from in inside into of off on out over through to under up upon with ETA There are others; these are just the most common ones.
ETA When you have two words used together as one verb (but contain a "preposition") such as call up, sit down, speak out, etc., those are not really prepositions on the end. These combinations are part of GERMAN grammar that became infused with our grammar.
When you have a preposition, you also will have an object of the preposition, thus a prepositional phrase.
Prepositional phrases are not part of the sentence pattern.
What fractional part of the pets is birds? = What fractional part is birds?
part=N1(subject) is=LV linking verb birds=N1(predicate noun/same as subject) (Note that part and birds are the same thing.)
ETA
BTW, that old rule that says that you should never end a sentence with a preposition is obsolete. It's perfectly correct to separate the preposition and its object in a sentence, e.g., With whom did Mary go? sounds stuffy doesn't it, so... Whom did Mary go with?/Mary went with whom? Both are correct.
"A preposition is something you never end a sentence with."
It is wrong though to say something like Where's it at? because you don't need the at (a preposition), and some smart aleck will say, "It's behind the at." So just say Where is it?
