The underlined part in ‘It seems quite obvious to me when it was done’ can be analyzed as

unless

as

so that

prepositions always go with a noun or nominal

the noun following a preposition is in function OP

prepositions is a sub-class of closed class

True

False

A noun is a word in the position of subject of the verb in a sentence.

A noun is a word standing for another word as subject of the verb

A noun must be always preceded by a determiner

adverbs may modify a verb

adverbs may modify an adjective

adverbs describe the circumstances of an action

linking verbs link the complement to its subject

linking verbs describe the state of its subject

linking verbs are usually followed by adjectives or nouns

does not agree with the subject

is the main verb in a sentence

is the auxiliary in the sentence

simple

complex

compound

agrees with the subject

is the main verb in a sentence

is the auxiliary in the sentence

infinitive

gerund

present participle

finite

sometimes non-finite

sometimes finite

simple

complex

compound

is always auxiliary

is always finite

is always non-finite

may be auxiliary or main verb