He is working in this company for ten years. (Improve the underlined part)

• A. works
• B. has been working (Answer)
• C. worked
• D. No improvement

'Has been working' (present perfect continuous) is correct for an action that started in the past and continues now. 'For ten years' signals duration.

She is more smarter than her sister. (Improve)

• A. more smart
• B. most smart
• C. smarter (Answer)
• D. No improvement

'Smarter' is already comparative. Adding 'more' creates a double comparative, which is incorrect.

The teacher told the students to not talk in class. (Improve)

• A. not to talk (Answer)
• B. to not talking
• C. don't talk
• D. No improvement

In reported speech with 'tell + object + infinitive', the negative is 'not to + verb', not 'to not + verb'.

He prefers tea over coffee. (Improve)

• A. than coffee
• B. to coffee (Answer)
• C. above coffee
• D. No improvement

'Prefer + noun + to + noun' is the correct structure. Not 'over' or 'than'.

She could not help to cry when she heard the bad news. (Improve)

• A. could not help cry
• B. could not help crying (Answer)
• C. could not help but cry
• D. No improvement

'Cannot help + gerund' is the correct structure. 'Cannot help crying' means unable to stop crying.

He is one of the best student in the class. (Improve)

• A. one of the best students (Answer)
• B. one of best student
• C. one among the best student
• D. No improvement

'One of the + superlative + plural noun' is the correct structure.

I have met him yesterday. (Improve)

• A. have been meeting
• B. met (Answer)
• C. had met
• D. No improvement

'Yesterday' is a specific past time marker. Present perfect cannot be used with specific past time. Simple past 'met' is correct.

She is too weak that she cannot walk. (Improve)

• A. so weak that (Answer)
• B. very weak that
• C. such weak that
• D. No improvement

'So weak that' is the correct structure for result clauses. 'Too weak to walk' is another correct form.

He is suffering with fever since yesterday. (Improve)

• A. suffering by fever
• B. suffering from fever (Answer)
• C. suffering in fever
• D. No improvement

'Suffer from' is the correct collocation for illness.

Neither he nor his friends was present. (Improve)

• A. were present (Answer)
• B. is present
• C. has been present
• D. No improvement

With 'neither...nor', verb agrees with the nearest subject (friends = plural), so 'were' is correct.