In the following question, select the alternative which will best improve the bracketed part of the sentence. In case no improvement is needed, select "No improvement": (Up to) the time he was not here, we were not sure if he would actually come.

Introduction / Context:
This question tests your knowledge of correct prepositions and conjunctions used to express time in English, particularly when we want to say that something continued up to a certain point. It also indirectly checks your sense of tense sequence in complex sentences where one action happens before or up to another action in the past.

Given Data / Assumptions:

• The original sentence uses the bracketed word “Upto”, which is a very common incorrect spelling in Indian English.
• The structure of the sentence is: “(Up to) the time he was not here, we were not sure if he would actually come.”
• We are only asked to improve the bracketed part; the rest of the sentence remains as it is.
• We assume a formal written English context, like an exam or official passage.

Concept / Approach:
To talk about something continuing up to a point in time, English normally uses “till” or “until”. “Up to” is also possible in some structures, but here the combination “Up to the time he was not here” is awkward and non-standard. Between “till” and “until”, “until” is considered slightly more formal and fits very naturally before “the time he was not here”. Therefore, replacing “Upto” with “Until” gives the most grammatically correct and idiomatic sentence in a formal context.

Step-by-Step Solution:
Identify the function of the bracketed word: it introduces the time up to which we were not sure.Recognise that “Upto” is incorrect; the standard spelling is “up to” (two words).Check the options: “Till”, “To”, “Until”, and “No improvement”.“To the time he was not here” is ungrammatical and incomplete for this meaning.“Till the time he was not here” is understandable but slightly less formal.“Until the time he was not here” is smooth, correct, and formally appropriate.Therefore, “Until” is the best replacement for the bracketed part.

Verification / Alternative check:
Read the improved sentence: “Until the time he was not here, we were not sure if he would actually come.” A better modern version would be, “Until he arrived, we were not sure if he would actually come,” but within the limits of the question, simply changing “Upto” to “Until” corrects the obvious error and preserves the intended meaning. “No improvement” cannot be correct, because “Upto” itself is wrong in spelling and usage.

Why Other Options Are Wrong:
“Till” is not wrong in meaning, but exams usually expect the more formal “until” in such structures. “To” does not work here as a time conjunction. “No improvement” would leave us with the incorrect “Upto”, which is non-standard. Only “Until” fully satisfies the requirements of formal grammar and idiomatic usage.

Common Pitfalls:
Candidates often treat “upto” as one word and assume it is acceptable; however, the correct form is “up to”, and in many exam questions it is deliberately replaced by “till” or “until” to create a more standard structure. Also, remember that “until” is usually preferred in formal writing over “till”.

Final Answer:
The bracketed part should be replaced with Until.