This is a simple alternating addition and subtraction series.

Correct Option: B

This is a simple alternating addition and subtraction series. In the first pattern, 3 is added; in the second, 2 is subtracted.

This is a simple division series. Each number is divided by 5.

Correct Option: A

This is a simple division series. Each number is divided by 5.

This is a simple multiplication series.

Correct Option: C

This is a simple multiplication series. Each number is 3 times more than the previous number.

In this series, each number is repeated,

Correct Option: B

In this series, each number is repeated, then 13 is subtracted to arrive at the next number.

In this alternating repetition series, the random number 21 is interpolated every other number into an otherwise

Correct Option: C

In this alternating repetition series, the random number 21 is interpolated every other number into an otherwise simple addition series that increases by 2, beginning with the number 9.