The idea of “measuring” other pricing patterns is out of place. Measuring other pricing patterns connotes a desire to assess how other pricing patterns compares to some idealized or especially good pricing pattern. That’s not the sense in which “standard” is used here, because there’s no suggestion that there is some ideal or desirable pattern of price movements.

“Commonly agreed-upon” doesn’t fit here, because there’s no indication that people agree to a particular pricing pattern. The price changes of a flower in the market are simply things that occur due to various economic factors. We’re given no reason to think people agree to pricing patterns. If you interpret “agreed-upon” in the sense that people might agree that there exists a typical pricing pattern for new flowers, (B) is still incorrect, because we don’t know what other people think about the pricing pattern described by Garber. “Standard” isn’t being used in the sense of a standard that we try to meet or hold ourselves to; it’s being used in the sense of “typical.”

The idea of acceptability doesn’t fit in connection with the phrase. Garber is simply describing what he views to be a pattern that is observed in a particular circumstance — when very prized flower varieties are developed. Garber doesn’t express any opinion about the acceptability of the prices (i.e. whether they should be higher, whether they’re just right).

This best captures the meaning. Garber describes what he views to be the standard pricing pattern for new varieties of flowers: “When a particularly prized variety is developed, its original bulb sells for a high price.” This suggests that by “standard pricing pattern,” the author means this pattern is something that isn’t unique or random; it’s something that Garber thinks we can expect to occur whenever a very prized flower bulb is developed.

The “standard pricing pattern” is not an example of something broader. Although we can say that the pricing pattern observed in the tulip market is an example of what Garber views to be a standard pricing pattern, the question asks about the meaning of “standard pricing pattern.”