10.50 verb agreement
Usually a plural form of 'be' is used if the noun group after it is plural.
You use a singular form of 'be' when you are giving a list of items and the first noun in the list is singular or uncountable.
Note that you use a plural form of 'be' in front of plural quantifiers beginning with 'a', such as 'a number of', 'a lot of', and 'a few of'.
You also use a plural form of 'be' in front of numbers beginning with 'a', such as 'a hundred', 'a thousand', and 'a dozen'.