What Is the 1/X Problem as It Applies to Averaging

What is the 1/X problem as it applies to averaging P/E ratios?

A) It refers to the fact that a P/E ratio may not make sense when a firm's earnings are very small, and including such firms when calculating an industry average can result in an
Invalid comparison P/E.
B) It refers to the fact that it may be difficult to find a good comparable firm ("Firm X") in a single line of business.
C) It refers to the fact that there are a large number of firms in most industries, which results in an enormous amount of data collection when trying to determine an industry average
P/E ratio.
D) It refers to the fact that the expected eternal earnings growth rate ("X") is difficult to estimate.