The answer would be the 4th option. (Rainwater soaking into the ground). Soil erosion is commonly caused by rainwater soaking into the ground.
LEDC means that a country is a developing country (as opposed to a developed country). This distinction is connected to the Brandt line which divides the world into developed and developing country, and India is south of this line (=LEDC, less developed country). Some reasons for this is malnutrition, high child mortality and short life expectancy.
Protozoa are single celled organisms. They come in many different shapes and sizes ranging from an Amoeba which can change its shape to Paramecium with its fixed shape and complex structure. They live in a wide variety of moist habitats including fresh water, marine environments and the soil.
An acute angle is less than 90 degree ;)
