Concept:Subject-verb agreement: the verb must match the number of the subject.Explanation:The subject is the phrase "All we need".It is treated as singular because it refers to one whole idea or single requirement.So a singular verb is needed."is" is the correct singular present-tense verb."are" and "were" are plural verbs, so they do not agree with the singular subject."was" is singular but past tense, so it is not the best choice here.Answer:C. is