"I feel sick when I see blood."
Translation:Mothaím tinn nuair a bhfeicim fuil.
To my knowledge, nuair takes a direct relative clause beginning with the particle a, which lenites its verb (in this case, a verb in the present tense that isn’t negated) rather than eclipsing it. An indirect relative clause would cause its verb to eclipse, but I don’t think that nuair can introduce an indirect relative clause.
EDIT: The direct relative particle a doesn’t mutate past indicative autonomous verb forms, or verb forms that begin with d’.
In my view, yes, it’s an error in the exercise. A relative clause is a subordinate clause that refers back to a word in the primary clause. The difference between a direct relative clause and an indirect relative clause in Irish is that a direct relative clause refers back to a subject or direct object in the primary clause, while the indirect relative clause refers to a genitive or back to a pronoun that itself refers back to the primary clause. An example sentence with both types of relative clauses is Tá an fear a fheicim a dtáinig a bhean chéile ag gáire. (“The man who I see whose wife arrived is laughing.”). Its direct relative clause is a fheicim (“who I see”), and its verb is lenited; its indirect relative clause is a dtáinig a bhean chéile (“whose wife arrived”), and its verb is eclipsed. Both relative clauses refer back to an fear.
The key word is "before" - sula means "before".
sula n-éirím ar maidin, mothaím tinn - "before I get up in the morning, I feel sick"
If the verb is a regular verb in the past tense, sula becomes sular:
sular éirigh mé ar maidin, mhothaigh mé tinn - "before I got up this morning, I felt sick"
You can't use sula to say "when".