Select the most appropriate option to substitute the underlined segment in the given sentence. If no substitution is required, select 'No substitution required'.

The team leader was discussing about the new project details with the client.

The correct option to substitute the underlined segment is was discussing.

Step-by-step Explanation:

1. Analyze the verb 'discuss':
The verb discuss is a transitive verb, which means it takes a direct object directly after it without requiring a preposition. The word discuss itself means "to talk about something".

2. Identify the redundancy:
Using the preposition about right after discussing creates redundancy because "discussing" already includes the meaning of "talking about". Therefore, saying "discussing about" is grammatically incorrect.

3. Evaluate the options:
- had been discussing about: Incorrect due to the redundant preposition "about".
- was discussing: Correct because it removes the unnecessary preposition "about" and properly connects the transitive verb "discussing" to its direct object "the new project details".
- was discussing regarding: Incorrect because "regarding" is another redundant preposition here.
- had a discussion about: While "discussion about" is grammatically valid when "discussion" is used as a noun, the tense shift is unnecessary and "was discussing" provides the most direct and accurate substitution preserving the original past continuous tense.

Hence, replacing was discussing about with was discussing makes the sentence grammatically sound: "The team leader was discussing the new project details with the client."