Select the option that can correctly replace the highlighted word or phrase and make the sentence grammatically correct. Mr. and Mrs. Singh have been married (since) thirty years.

Correct option is C

The correct phrase is "for thirty years" because "for" is used when referring to a duration of time. "Since" is used with a specific point in time (e.g., since 1993), whereas "for" is used to express the length of time (e.g., for 30 years). Hence, the correct sentence is: Mr. and Mrs. Singh have been married for thirty years.
Explanation of options: (a) from – "From" requires a starting point and usually a counterpart "to" or "until" (e.g., from 1990 to 2020). It cannot be used alone to express duration. So it does not suit the sentence structure here.
(b) till – "Till" means "until" and indicates the end point of a time period, not the duration itself. It cannot replace “since” in a sentence meant to show how long something has continued. So, it's not applicable.
(c) for – This is the correct option. "For thirty years" expresses a duration of time and correctly complements the present perfect tense "have been married." This preposition is grammatically accurate for describing ongoing states.
(d) until – Like "till," "until" is used to refer to the end point of an action or state. It cannot express a span of time that continues from the past into the present. Hence, it's incorrect here.