Select the most appropriate idiom for the underlined part in the given sentence:
Amar was left in a difficult situation by his business partners.

The correct answer is High and dry.

Let us break down the meanings of the given idiomatic expressions to find the one that best fits the underlined phrase "in a difficult situation":

1. High and dry: This idiom means to be left in a difficult, helpless, or abandoned situation without resources or support. For example, if someone is left "high and dry" by their business partners, they are left stranded or in a tight spot. This directly matches the meaning of "in a difficult situation".

2. Hard and fast: This refers to rules or regulations that are strict, fixed, and cannot be changed or modified.

3. Head and shoulders above: This means to be significantly better or superior to others in a particular field or activity.

4. Heart and soul: This means with complete commitment, energy, and enthusiasm.

Therefore, the most appropriate idiom to replace "in a difficult situation" is High and dry.