The answer is 5.
The missing number is the number that completes the sequence. The sequence is a list of numbers that follow a certain pattern. In this case, the pattern is that each number is 1 more than the previous number. So, the first number is 1, the second number is 2, the third number is 3, and so on. The missing number is the number that comes after 4. Since 5 is 1 more than 4, it is the missing number.
A. 7 is not the missing number because it is not 1 more than 4.
B. 4 is not the missing number because it is the number that comes before the missing number.
C. 5 is the missing number because it is 1 more than 4 and it comes after 4.
D. 6 is not the missing number because it is 2 more than 4.