Select the most appropriate option that can substitute the underlined segment in the given sentence.
Little that I knew of the English language was not sufficient to make me an English teacher.

The correct option to substitute the underlined segment is The little.

Explanation:
Let us understand the difference between the determiners used with uncountable nouns:

1. Little: Means 'hardly any' or 'almost nothing'. It has a negative connotation.
2. A little: Means 'some quantity', though not much. It has a positive connotation.
3. The little: Means 'not much, but all that is available/specified'. It refers to a specific small amount that exists.

In the given sentence, the speaker refers to the specific, limited knowledge of the English language that they possessed ("that I knew of the English language"). Since it points to all of the small amount of knowledge the person had, the definite article modifier "The little" is required.

Therefore, the corrected sentence is:
"The little that I knew of the English language was not sufficient to make me an English teacher."