Because there is an opening for each leg.
"There is a pair of trousers" is correct because "pair" is a singular noun and takes a singular verb.
The term "knickers" is believed to be a shortening of the word "knickerbockers," which were a type of baggy trousers that reached just below the knee. The name "knickerbockers" is said to originate from the last name of an early Dutch settler in New York, Washington Irving's "Diedrich Knickerbocker." Over time, the term "knickers" became a colloquial term for women's undergarments in the UK.
A pair of scissors is the singular form.
they called their dolls poppets and their marbles knickers
Boots is plural. Boot is singular.BUT - 'a pair of boots' is singular, because you are referring to the pair, which is just one.
They sell knickers in target. But some of them dont have knickers
The singular possessive form is pants'.The noun pants is a short form for a pair of pants; the noun pants does not change from singular to plural, the word pair is the part of the term that changes: a pair of pants, two pairs of pants.
Only if you consider a "pair of pants" a singular noun. (No.)
who invented the knickers and why.
I have knickers on me.
Pair is a singular noun, so when it's the subject it takes a singular verb: pair has "This pair of chickens has a bad attitude." previous answer misses the point entirely: it depends on how it is used, eg; She has a pair of stockings, they have a pair of stockings. Previous amendment to this answer misses the point entirely. The question isn't asking if it's "has a pair" or "have a pair". It does depend on the context, however - If you're considering the items in the pair individually, use it like a plural subject, but if it's a single entity (pair of scissors, for example), use it like a singular subject.
Singular: book / Plural: books Singular: cat / Plural: cats Singular: child / Plural: children Singular: foot / Plural: feet