The purpose of genetically modifying brinjal and cotton as Bt-brinjal and Bt-cotton was to make them pest-resistant.
Option 1: Drought-resistant - This option suggests that the genetically modified crops were modified to withstand drought conditions. However, there is no mention of drought resistance in the question. Therefore, this option is not the correct answer.
Option 2: High-yielding - This option suggests that the genetically modified crops were modified to increase their yield. While genetically modified crops often have increased yield potential, the specific purpose mentioned in the question is pest-resistance, not high-yielding. Therefore, this option is not the correct answer.
Option 3: Pest-resistant - This option correctly states that the purpose of genetically modifying brinjal and cotton was to make them resistant to pests. The modification involved introducing the Bt gene from the bacteria Bacillus thuringiensis, which produces a protein toxic to certain pests. Therefore, this option is the correct answer.
Option 4: Short-duration crops - This option suggests that the genetically modified crops were modified to have a shorter growth duration. However, there is no mention of short-duration crops in the question. Therefore, this option is not the correct answer.
In summary, the correct answer