Correct Answer:
B. 79
To solve this sequence, we need to identify the mathematical rule connecting each number to the next. Let's examine the progression: from 4 to 9, from 9 to 19, and from 19 to 39. The pattern is consistently 'multiply the previous number by 2, then add 1'.
- 4 x 2 + 1 = 9
- 9 x 2 + 1 = 19
- 19 x 2 + 1 = 39
Applying this rule to the last number in the sequence, 39, we perform the calculation: 39 x 2 + 1 = 78 + 1 = 79. Therefore, option B is the correct answer. Options A (59), C (61), and D (81) are incorrect because they do not adhere to the established 'multiply by 2 and add 1' pattern of the sequence.