Select the most appropriate option to substitute the highlighted segment in the given sentence. If there is no need to substitute it, select ‘No substitution required’.
Since 10 o’clock in the morning he worked on this design.

Correct option is C

Option (c) "he has been working" is the correct answer.
· Explanation: The sentence indicates an action that started in the past and is still ongoing. The present perfect continuous tense ("has been working") is used to describe such actions, especially when they have been occurring from a specific time in the past (since 10 o’clock in the morning) up to the present.
· Grammatical rule used: The present perfect continuous tense is formed using "has/have been" + the present participle (verb + ing) and is used to express an action that began in the past and continues into the present.
· Example:
· Incorrect: Since 10 o’clock in the morning, he worked on this design.
· Correct: Since 10 o’clock in the morning, he has been working on this design.