Question

Organic farming is raising crops through use of

• A. Resistant varieties
• B. All of the above
• C. Biofertilisers
• D. Manures
  

Answer 1

The correct option is B All of the above

Organic farming
Organic farming is a type of sustainable farming method that uses natural fertilisers and pesticides usually of biological origin, thus preventing pollution and harm to the environment.
Following are the major approaches used:

1. Biofertilisers
2. Manures
3. Resistant varieties

Biofertilisers
Biofertilisers are the fertilisers of biological origin which don't contain harmful chemicals. Administration of biofertilisers ensures enhanced fertility of the soil without causing harm to the environment. For example, association of $Anabaenaazollae$ with $Azolla$.

Manures
Manures are the decompost formed out of dead and decaying plants and animals as well as its derivatives. These are organic in nature and improve soil fertility.

Resistant varieties
Resistant varieties of crops are being developed by genetic modifications to confer desired qualities like disease resistance, better yield etc. to the plants. For example, Bt cotton is genetically engineered cotton having the $cry$ gene of a bacterium, $Bacillusthuringiensis$. The $cry$ gene expresses the inactive toxin, which when digested by the insects, gets activated in their gut having alkaline pH. This causes cell lysis and death of the insect/ pest.

Final answer
(D) All of the above