Find the appropriate meaning of the underlined idiom. A true friend will stand…

Concept

An idiom is a fixed expression whose overall meaning cannot be worked out by adding up the literal meanings of its individual words; you must learn the conventional sense as a whole. To choose the right meaning, replace the idiom with each candidate phrase and keep the one that preserves the sentence's intended sense.

Application

The idiom through thick and thin conventionally means staying loyal and steadfast in every kind of situation — both the good ("thick") and the bad ("thin"). In "A true friend will stand by you through thick and thin," it describes a friend who remains by your side no matter what happens. The phrase that captures this whole-situation loyalty is "under all circumstances".

Contrast

Why the other readings fall short:

• "in difficult times" — covers only the "thin" (bad) half; the idiom also includes the good times, so this is too narrow.

• "at the last moment" — describes timing (suddenly, just in time), which is unrelated to steadfast loyalty.

• "during summer time" — a literal weather/season reading; the idiom has nothing to do with the seasons.