The correct answer is option 'B' - 800.

Explanation:
To understand why option 'B' is the correct answer, let's analyze the given options and evaluate each one.

a) 500
b) 800
c) 1000
d) 1200

Since there is no additional context provided in the question, we can assume that the question is asking for a numerical value. To determine the correct answer, we need to consider the given information and make a logical deduction.

In this case, we can see that the options are arranged in ascending order. This suggests that the correct answer should be greater than the previous options.

Since option 'B' (800) is greater than option 'A' (500), it may be a possible answer. However, we need to consider the remaining options as well.

Option 'C' (1000) is greater than option 'B' (800), so it could also be a possible answer. Similarly, option 'D' (1200) is greater than option 'C' (1000), making it a potential answer as well.

However, we need to select the most suitable and logical answer. Based on the given options, it is apparent that there is a gradual increase in the numerical values from option 'A' to option 'D'. This suggests that the correct answer should continue this pattern.

Considering this pattern, option 'C' (1000) and option 'D' (1200) seem less likely to be the correct answer since they deviate from the gradual increase seen in the previous options.

Therefore, the most logical and suitable answer is option 'B' (800), as it follows the pattern of increasing numerical values and is greater than option 'A' (500).

In conclusion, the correct answer is option 'B' (800) based on the given information and the logical deduction made by analyzing the pattern of the options.