data

In formal writing, it’s probably best to treat this word as a plural. Thus: the data are.

The singular is datum, but in nonscientific circles, you’ll probably sound pretentious if you use datum.

Usage panels now increasingly recognize that data can refer to a mass of information and thus can take a singular verb.

Consider this usage note on Dictionary.com:

The word data is the plural of Latin datum, “something given,” but it is not always treated as a plural noun in English. The plural usage is still common, as this headline from the New York Times attests: “Data Are Elusive on the Homeless.” Sometimes scientists think of data as plural, as in These data do not support the conclusions. But more often scientists and researchers think of data as a singular mass entity like information, and most people now follow this in general usage. Sixty percent of the Usage Panel accepts the use of data with a singular verb and pronoun in the sentence Once the data is in, we can begin to analyze it. A still larger number, 77 percent, accepts the sentence We have very little data on the efficacy of such programs, where the quantifier very little, which is not used with similar plural nouns such as facts and results, implies that data here is indeed singular.

Dictionary.reference.com/browse/data.