The correct answer is B. Large numbers.
The law of large numbers states that the more times an event is repeated, the closer the actual results will get to the expected results. This is because, as the number of trials increases, the effects of chance will cancel each other out, and the results will become more predictable.
Insurance companies use the law of large numbers to calculate the probability of an event occurring and to set premiums. By pooling the risks of a large number of people, insurance companies can spread the cost of losses over a wider group, making it more affordable for individuals to purchase insurance.
Option A, inertia, is the tendency of an object to resist changes in its motion. This is not relevant to the question of how to make accurate statistical estimates.
Option C, large groups, is a related concept, but it is not the same as the law of large numbers. A large group of people may not necessarily be representative of the population as a whole, and therefore the results of a study conducted on a large group may not be accurate.
Option D, none of the above, is also incorrect. The law of large numbers is the correct answer to the question.