Glass's
The singular possessive form for the noun clock is clock's.
The singular noun form is glass.There are two accepted forms for possessive singular nouns that end with an s:Add an apostrophe (') after the existing s at the end of the word:glass'Add an apostrophe s ('s) after the existing s at the end of the word:glass'sExamples:The glass' monogram is that of my grandfather.The glass's monogram is that of my grandfather.
Quantum is singular, not singular possessive. The singular possessive form is quantum's.
The possessive form for the singular noun speed is speed's.Example: This device will measure your speed's velocity.
you add a 's that's all and your word becomes speed's
The possessive form for the singular noun glass is glass's (just as you have it in your question).The plural form is glasses. The plural possessive form is glasses'.Example: I like these glasses' pattern the best.
The singular possessive form is week's.
The singular possessive form is classmate's.
The singular possessive form of the noun mirror is mirror's.The plural form of the noun mirror is mirrors.Thee plural possessive form is mirrors'.Examples:The mirror's frame cracked and the glass fell to the floor. (singular)All of the mirrors' reflections gave varying perspectives of the room. (plural)
The possessive form is Amos's.
The singular possessive form for the noun gypsy is gypsy's.
The singular possessive form for country is county's.
The singular form for the plural noun countries is country; the singular possessive form is country's.
singular possessive: boy'splural possessive: boys'
The singular possessive form is aircraft's.
The singular possessive form is frontiersman's.
The singular possessive form is contralto's.