Each of the following sentences contains a highlighted section that may be grammatically incorrect. From the options provided, select the one that best corrects the highlighted portion. If the sentence is already correct, select "No improvement needed".

A devious manager, the dishonest supervisor continued to deny mistreat even though there were multiple complaints.

The correct option is to deny mistreating even though.

Step-by-Step Breakdown:

1. Verb Pattern with "deny":
The verb deny is transitive and is followed by a gerund (a verb ending in -ing acting as a noun) when specifying an action being denied. Therefore, the base verb form "mistreat" is incorrect in this context and must be changed to the gerund form mistreating.

2. Infinitive Structure "to deny":
The main verb continued takes an infinitive (to + verb) or gerund (continued denying). In the given options, the structure to deny is correctly formed with the base infinitive deny, not "to denying".

3. Conjunction Choice ("even though"):
The phrase even though is a standard subordinate conjunction used to express contrast. The phrase "even although" in one of the options is non-standard and grammatically redundant.

Combining these corrections gives the phrase: to deny mistreating even though.