Select the most appropriate option to transform the given sentence into reported speech.
Ram said, "I worked with a Japanese company last month."

Correct option is C

The correct option is (c) Ram said that he had worked with a Japanese company the previous month.

Explanation:
The given sentence is in Direct Speech. While converting it into Indirect (Reported) Speech, the following rules apply:

Rules Applied in Conversion (Direct → Indirect):

• Tense Change: Simple Past (worked) → Past Perfect (had worked), since the reporting verb said is in the past tense.
• Pronoun Change: I → he (third person, referring to Ram).
• Time Expression Change: last month → the previous month (time expressions shift back in reported speech).
• Conjunction: that is added after the reporting verb.
• Quotation marks are removed in reported speech.

• (a) has worked... previous month – Incorrect tense (present perfect); should be past perfect. Also, previous month without the is grammatically incomplete.
• (b) has been worked – Grammatically incorrect passive form; does not apply here.
• (d) I worked – Pronoun is not changed; keeping I in indirect speech is grammatically incorrect.