|Collective nouns, or collectives (family, team, couple, etc.), tend to be
plural when the component members are considered separately and singular
when the group is handled as a unit:
a score were present
marches on its stomach
The plural often prevails when humans are
The couple are. . . .
The decision between singular and plural is frequently writer's choice.
Once the number is established, be consistent:
My family trusts only
people it knows
my family trust only people they know
Dr. Smith's team
works long hours in the hot sun,
but it [not they] always maintains an esprit de corps.
Piersma's team works fast; the scientists [not they] prepare
a net to be fired by mortars
The enemy wasn't interested merely in conquest; it [not they] wanted
to wipe Aguateca off the map.
Generally speaking, a number, a fraction, or a quantity of things is
singular if considered as a mass (ten gallons is enough) and plural if
considered as separate units (ten dishfuls were slowly doled out).
Generally use a plural verb when human beings are implied:
Half the wine is enjoyed ...
Half of these people are engaged ...
35 percent of the bread goes ...
35 percent of the grapes go ...