Which one of the following is the correct sequence of the following topographical features found from upper to lower course of a river?

Rapids-Ox-bow lake-Estuary. Rapids are sections of a river where the river bed has a relatively steep gradient, causing an increase in water velocity and turbulence. An oxbow lake is a U-shaped lake that forms when a wide meander from the main stem of a river is cut off, creating a free-standing body of water. An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea.