Mathematics is not always an exact science.
"Mathematics" is a singular noun, so we use the singular form of the verb "is."
Mr. John, accompanied by several members of the committee, has proposed some changes of the rules.
"Mr. John" is the singular subject, so we use the singular form of the verb "has."
The flock of birds is circling overhead.
"The flock" is considered a singular collective noun, so we use the singular form of the verb "is."
The levels of intoxication vary from subject to subject.
"Levels" is a plural noun, so we use the plural form of the verb "vary."
The majority of the students believe him to be innocent.
"The majority" is considered a singular noun, so we use the singular form of the verb "believe."
The pair of pliers was on the table.
"The pair" is considered a singular unit, so we use the singular form of the verb "was."
The use of credit cards in place of cash has been increased rapidly in recent years.
"The use" is a singular noun, so we use the singular form of the verb "has been."
Advertisements on television are becoming more competitive than ever before.
"Advertisements" is a plural noun, so we use the plural form of the verb "are becoming."