To find the correct match of grammatical function with usage for the word "then," let's analyze each function:
- Noun: "Then" can function as a noun when referring to a specific time in the past or future. The example "I have not heard about him since then." matches this usage, so the correct pairing is 1-6.
- Adjective: "Then" acts as an adjective when preceding a noun to indicate a particular time, as seen in the sentence "He was the then King of Nepal." Hence, the match is 2-5.
- Adverb: When "then" is used as an adverb, it refers to a specific time or sequence of events. The sentence "He was not a graduate then." fits this function, indicating that "then" refers to a time in the past, so we match 3-8.
- Conjunction: "Then" serves as a conjunction when connecting sentences or clauses to show sequence or cause-effect. In "He is not feeling well, then how can he possibly go for the picnic.", "then" connects the reasoning, making 4-7 the appropriate match.
Therefore, the correct answer is: 1-6, 2-5, 3-8, 4-7.