A farm animal disease that results to abortion of pregnancy in cows is

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15. Mealybugs are common pests of rubber trees, feeding on sap and causing stunted growth or leaf distortion.

    The correct option is C.

    $$\boxed{\text{C. mealybug}}$$

16. A fish pond is best established on flat land. This ensures even water distribution, ease of construction, and minimizes erosion.

    The correct option is B.

    $$\boxed{\text{B. flat}}$$

17. Calopogonium mucunoides is a legume whose pods dry and split open with force, scattering seeds through an explosive mechanism.

    The correct option is D.

    $$\boxed{\text{D. Calopogonium mucunoides}}$$

18. Brucellosis is a bacterial disease in cattle that commonly causes abortions in pregnant cows, as well as infertility and reduced milk production.

    The correct option is A.

    $$\boxed{\text{A. brucellosis}}$$

19. Arachis hypogaea is the scientific name for groundnut or peanut, which is a widely cultivated food crop.

    The correct option is B.

    $$\boxed{\text{B. Arachis hypogaea}}$$

20. This question is not fully visible in the image.

21. Castration is a management practice involving the removal of testicles to alter an animal's characteristics (e.g., for meat quality or temperament), not a method of identification. Tagging, branding, tattooing, and ear notching are all methods used for identifying cattle.

    The correct option is E.

    $$\boxed{\text{E. castration}}$$

22. The pH scale ranges from 0 to 14, with 7 being neutral. Values below 7 are acidic. A pH of 2 is significantly below 7, indicating that the soil is strongly acidic.

    The correct option is A.

    $$\boxed{\text{A. strongly acidic}}$$