The luxuriant growth of natural vegetation in the tropical rainforest is due to  

1. fertile soil.

2. hot and wet climate throughout the year.

3. intense sunlight for photosynthesis.

4. seasonal change to facilitate nutrient absorption.

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A farmer in a semi-arid area claims that his farming practice is very environment-friendly. Which of the following practices on his farm can justify his claim? 

1. Planting a tree belt.

2. Practising crop rotation.

3. Carrying out a large scale irrigation system.

4. Using organic fertilizers.

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'Yakuts' are the nomadic herders of 

Which of the following are the characteristics of organic fanning?  

1. Use of chemical fertilizers to improve soil fertility

2. Frequent decomposing and fallowing.

3. Use of herbs to control pests.

4. Higher productivity per hectare.

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Permanent hardness of water is due to the presence of