Select the most appropriate adjective to fill in the blank. Simrin and Kannan…

Vocabulary-based fill-in-the-blank items are solved by comparing each candidate word's precise dictionary meaning against every logical requirement set by the rest of the sentence. The correct choice must be semantically consistent with the full context, not just a familiar-sounding word.

The sentence requires an adjective describing a personal connection between Simrin and Kannan that is strong enough to be unbreakable ("that nothing could break"). "Kindred" means very similar in nature, spirit, or feeling; closely related or akin (as in the common phrase "kindred spirits"). A bond rooted in this kind of deep natural affinity logically supports being described as unbreakable, so "kindred" satisfies the sentence's requirement.

• "Grave" means serious, solemn, or of great importance (as in a grave expression or a grave decision). It describes tone or gravity, not the closeness or durability of a personal relationship, so it does not fit "bond."

• "Frail" means physically weak, fragile, or easily damaged (as in a frail structure or frail health). This meaning is the opposite of what "that nothing could break" requires, so it directly contradicts the sentence.

• "Grumpy" means easily irritated, bad-tempered, or given to complaining (as in a grumpy mood or a grumpy reply). It describes a person's temperament, not the nature of a bond between two people.

The bond between Simrin and Kannan is described as unbreakable, which matches a connection rooted in deep natural affinity. The correct adjective is "kindred."