Which of the following actions could prevent mass-movement disasters?

Question:

Which of the following actions could prevent mass-movement disasters?(a)constructing building and roads in stream drainage paths

(b)removing trees from steep slopes

(c)educating people about the advantages of building on steep slopes

(d)digging a series of trenches to divert water around a slope

Answer:

"Digging a series of trenches to divert water around a slope"  could prevent mass-movement disasters

Explanation:

The trenches are made of 12 to 15 inches in width and at least 6-8 inches depth, can help in normal drainage problem. But in long, steep slopes and areas receiving heavy rainfall, digging of trenches is more advisable. It prevents the tripping over and falling down of people, it protects the runoff of edges and also collapsing. These trenches should be filled with coarse gravel or may be small stones. In the final labelling one or two inch of fine gravel or coarse sand. It will make the surface level which will allow the water to seep down.  

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

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