A majority of courts have followed Roe v. Wade. (Here, the courts have acted individually, in separate cases, not as a single group or mass. Thus, the verb have followed is plural.)But if the individual members of the group act as a unit, then you should use a singular verb. Study this example:
A group of Senators has decided to introduce the bill. (Here, the group acted as a unit. Thus, the verb has decided is singular.)In England, group nouns typically take a plural verb. Thus, across the pond, you'll hear:
The jury have reached their verdict.
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