If your subject consists of two or more nouns, you need to pay special attention to subject-verb agreement. If the nouns are connected by the coordinating conjunction and, use a plural verb.
Although accidents and congestion results from driving
itself rather than from fuel use, much of urban air pollution, greenhouse gas
emissions, and the economic burden of oil imports can all be tied directly to
fuel consumption.
Although accidents and congestion result from driving
itself rather than from fuel use, much of urban air pollution, greenhouse gas
emissions, and the economic burden of oil imports can all be tied directly to
fuel consumption.
--"Improving Automotive Efficiency," Scientific American (modified)
However, if the nouns connected by the coordinating conjunction and are generally thought of as one item, use a singular verb.
Macaroni and cheese are easy to make.
Macaroni and cheese is easy to make.
If the nouns are connected by the coordinating conjunction or, use a verb that agrees with the nearer noun.
Your advisor or your course instructor are required to
sign the form.
Your advisor or your course instructor is required to
sign the form.
If the nouns are connected by the correlative conjunction both . . . and, use a plural verb.
Both your advisor and your course instructor is required
to sign the form.
Both your advisor and your course instructor are
required to sign the form.
If the nouns are connected by the correlative conjunctions either . . . or, neither . . . nor, not only . . . but also, use a verb that agrees with the nearer noun.
Either your course instructor or three fellow students who know
your ability is required to sign the form.
Either three fellow students who know your ability or your course
instructor are required to sign the form.
Either your course instructor or three fellow students who know
your ability are required to sign the form.
Either three fellow students who know your ability or your course
instructor is required to sign the form.