Ascertain which noun is the subject of your sentence.
A reference list (singular subject) is (single verb) provided in the appendix.
The snails (plural subject) are (plural subject) lined up waiting for the race to start.
Collective nouns take a plural verb.
The aroma of baking cookies make my mouth water. (incorrect)
The aroma of baking cookies makes my mouth water. (correct)
Aroma is the subject of the sentence and agrees with makes. The word cookies is the object.
When two or more subjects are connected by the word and, use a plural verb.
Swimming and running is my favorite form of exercise. (incorrect)
Swimming and running are my favorite forms of exercise. (correct)
The red rose and the white gardenia is the flowers she chose for the wedding bouquet. (incorrect)
The red rose and the white gardenia are the flowers she chose for her wedding bouquet. (correct)
When two or more subjects are connected by either, or neither, or nor, use a singular verb.
Either Jacob or Louis are driving me to the station. (incorrect)
Either Jacob or Louis is driving me to the station. (correct)
Either Karla or Karen are joining the cycling team. (incorrect)
Either Karla or Karen is joining the cycling team. (correct)
And finally, those moody subjunctives. When the sentence addresses something that is doubtful, hypothetical, wished, requested, or imagined, then the opposite of the standard rule is true: singular subjects connect with plural verbs.
I (singular subject) wish the English language were (plural subject) easier to understand.
Here’s my favorite subjunctive mood sentence provided by song writer Tim Hardin and made famous by Gordon Lightfoot:
“If I (singular subject) were (plural verb) a carpenter, and you (singular subject) were (plural verb) a lady . . ..” If you were/are older than forty, I imagine you know the rest of the line.