indicative
The teacher asked for an example of a subjunctive relative clause.
They clearly had knowledge of subjunctive form, but not of its use with relative clauses.

SMART Vocabulary: related words and phrases

Linguistics: verb forms, tenses & types of verbs
accusative
art
bare infinitive
bent
continuous
copula
finite
gerund
modality
non-finite
non-progressive
passive
passivization
perfective
phrasal verb
present participle
the active voice
the future perfect
the past continuous
the past tense

subjunctive | American Dictionary

subjunctive
noun[ U ]
us/səbˈdʒʌŋk·tɪv/
grammar
the mood (= form) of a verb used to refer to actions that are possibilities rather than facts:
In the sentence "I wish I were rich," the verb "were" is in the subjunctive.

Examples of subjunctive

subjunctive
A survey on the subjunctive, returned by over 600 readers, showed it to be in a state of "active retirement".
Table 2 shows the number of children passing none, one or both cognitive tests, and the number of subjunctive relatives produced by those children.
It replaced subjunctive complements to intention-verbs (conatives, desideratives, and their negative counterparts).
Thus, complements of verbs such as ' hopes ' and ' wishes ' get the subjunctive because the world of somebody's hopes and wishes is not the actual one.
I am assuming that some subjunctive conditionals with impossible antecedents are non-trivially true.
If a child may have more occasions to use the subjunctive as it matures, then whatever invites subject deletion may involve more sophisticated social postures.
Similarly, the verbs in the subordinate clause were considered relevant only if they were in one of the indicative or subjunctive preterit forms.
She found that of all the opportunities children had to produce a sentence, children used the subjunctive as frequently as the indicative.
This has to be formulated in the subjunctive rather than in the indicative, but it ought not to remain a mere wish.
More generally, it seems that subjunctives may be finite or non-finite in the same language, with different interpretations in the two cases.
A study was designed to test the hypothesis that children's acquisition of subjunctive in relative clauses depends on their representational capacities.
Meanwhile, the pluperfect subjunctive continued in its same usage with the morphology cantasses.
Results indicate a strong correlation between children's ability to use the subjunctive mood in relative clauses and their capacity for understanding false beliefs.
The study aimed to examine the relationship between children's performance on false belief tasks and their ability to produce subjunctive relative clauses.
Table 1 shows that the ability to produce subjunctive relative clauses increases with age.
These examples are from corpora and from sources on the web. Any opinions in the examples do not represent the opinion of the Cambridge Dictionary editors or of Cambridge University Press or its licensors.