Water erosion does not appear as one single event, it develops in stages that get more severe over time, and this question checks whether you know that order.
- Splash erosion: caused directly by the beating action of individual raindrops on unprotected soil, breaking soil clumps apart and flinging particles a short distance. This is always the first stage since it needs nothing more than bare soil and rainfall.
- Sheet erosion: once loosened particles begin moving with a thin, even film of runoff water, a uniform layer of topsoil is stripped off the whole surface. This can only happen after splash has already loosened the soil, so it is the second stage.
- Rill erosion: as sheet flow keeps moving, it naturally gathers into many small, narrow channels wherever the land has slight low spots, cutting shallow rills that a farmer can still erase by normal tillage. This stage needs sheet flow to already be underway, so it comes third.
- Gully erosion: if the rills are left alone, repeated flow cuts them deeper and wider until they become gullies, too large to plough out. Since gullies grow out of neglected rills, this is the last and most damaging stage.
Because each stage is the direct outcome of the one before it, the sequence must run splash, sheet, rill, gully, which is (A), (B), (C), (D), option (1).
Let's summarize:
- Erosion severity grows from raindrop splash to sheet to rill to gully.
- Catching erosion at the sheet or rill stage is far cheaper to fix than after gullies have formed.
The correct order is (A), (B), (C), (D), option (1).