Under Inland Rule 35, a vessel at anchor in restricted visibility is required to ring the bell rapidly for about 5 seconds at intervals of not more than how long?

Why B is correct

33 CFR §83.35(g) specifies that a vessel at anchor shall ring the bell rapidly for about 5 seconds at intervals of not more than 1 minute. The 2-minute interval applies to underway fog signals, not the anchor bell.