This is a test of commonsense with single/multi-choices. Complete the next sentence:

How to get irises to bloom
Be aware that irises need to be divided.
The first and most likely cause for irises failing to bloom is overcrowding. Irises must be dug up, divided and replanted every three to four years.

Pick from: (a). The reason why irises are not uniformly divided are are that the species are crowded and ecodegradable. Since irises become so dense in multitudes they, even you, are required to divide them for optimum quality. (b). If this does not happen, it becomes less likely that your irises will bloom. Cut the leaves down to a height of six inches. (c). It is always wise to divide irises once a year, even if they were put in pots at the end of the growing season. This will maximize the nutrients the irises provide and prevent overcrowding. (d). Move larger irises up or down back into the original row, below the initial row. Similar-sized irises need to be spaced across the transplanting rows.
The answer is:
(b).