Those … are very beautiful.

Analyze the question: The sentence "Those ____ are very beautiful" needs a phrase that shows possession and fits grammatically after "Those."

Concept: "Those" is a demonstrative determiner. It can be followed directly by a plural noun ("Those flowers"). If the noun is followed by "of," the possessive must be a double possessive, like "of ours," "of hers," or "of mine." In that case the possessive pronoun is used on its own.

Check each option:

• A. "Flowers of ours" gives "Those flowers of ours are very beautiful." This is a correct double possessive, and "ours" is the proper independent possessive pronoun. ✔
• B. "Flowers of her" is wrong. After "of" you need the possessive form "hers," not the object pronoun "her."
• C. "Flowers of her's" is wrong. "Hers" never takes an apostrophe.
• D. "Our flowers" gives "Those our flowers are very beautiful." This is wrong because two determiners ("those" and "our") cannot stand together before a noun. It would have to be "Those flowers" or "Our flowers."

Tip: Never put two determiners (this/that/those/these + my/our/your/her) before the same noun. Use the double possessive instead: "those friends of mine," "that book of hers," "these shoes of ours." Also remember that none of the independent possessive pronouns (hers, ours, yours, theirs) takes an apostrophe.