Explanation:

A. uncertain: 'Uncertain' means not known or definite. This is not the meaning of the idiom.\nB. inseparable: 'Inseparable' means unable to be separated or treated separately. This is not the meaning of the idiom.\nC. almost nothing: While someone 'not worth their salt' might be considered of little value, the idiom specifically refers to their competence or worthiness in a role, not their monetary value as 'almost nothing'.\nD. not deserving: The idiom 'not worth one's salt' means that someone is not good enough at their job or not deserving of their position, pay, or the benefits they receive because they are not performing adequately. This is the precise meaning of the idiom.