The proteins encoded by the genes cryIAb and cryIIAb control:(A) Cott…

The correct answer is Option (3) → (A) and (B) only

Bt crops carry genes taken from the bacterium Bacillus thuringiensis. These cry genes code for Cry proteins that are poisonous to certain insects. Each toxin acts only on a particular group of insects, so the gene is chosen to match the crop and its pest.

(A) Cotton bollworm — Correct. The protein coded by cryIIAb (together with cryIAc) controls the cotton bollworm.

(B) Corn borer — Correct. The protein coded by cryIAb controls the corn borer.

(C) Aphids — Incorrect. These cry genes are not used against aphids. Aphids are usually kept in check by biocontrol, for example by ladybird beetles.

(D) Mosquitoes — Incorrect. The proteins of these two genes are linked with crop pests (the bollworm and the corn borer), not with mosquitoes.

NCERT Extract:
Biotechnological Applications in Agriculture – “… Specific Bt toxin genes were isolated from Bacillus thuringiensis and incorporated into the several crop plants such as cotton (Figure 10.1). The choice of genes depends upon the crop and the targeted pest, as most Bt toxins are insect-group specific. The toxin is coded by a gene cryIAc named cry. There are a number of them, for example, the proteins encoded by the genes cryIAc and cryIIAb control the cotton bollworms, that of cryIAb controls corn borer.”