Numerical Reasoning - Number Series

Find the missing number in this series:

13  14  ?  16  17  18

A: 14

B: 15

C: 16

D: 17

E: none of these

Find the missing number in this series:

2  X  3  X  4  X  ?

A: 4

B: 5

C: 6

D: 7

E: none of these

Find the missing number in this series:

1  1  2  2  3  3  4  4  ?

A: 4

B: 5

C: 6

D: 7

E: none of these

Find the missing number in this series:

2  4  6  ?  10

A: 7

B: 8

C: 9

D: 10

E: none of these