12
5
8
1
Answer is Wrong!
Answer is Right!
The answer is 5.
The missing number is the sum of the first two numbers in the sequence, minus the third number. In this case, the first two numbers are 1 and 2, and the third number is 3. Therefore, the missing number is $1 + 2 – 3 = 5$.
Option A is incorrect because 12 is not the sum of the first two numbers in the sequence.
Option B is incorrect because 5 is the sum of the first two numbers in the sequence.
Option C is incorrect because 8 is not the sum of the first two numbers in the sequence.
Option D is incorrect because 1 is not the sum of the first two numbers in the sequence.