What is generally a safe frequency of activity for a work out? once a week, once or twice a week, three times a week, or three to five times a week?​

Which is one way that sinkholes can form? a) tornadoes touch down and destroy trees and brush b) rivera overflow during a storm and wash away nearby land c) rainwater flows away from a depression in the ground d) groundwater dissolves the limestone and other rocks in the ground