The statements are:
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(I) Correct. Sacculina, a parasitic barnacle, sterilizes its host. It infests crabs and manipulates their reproductive system, effectively rendering them sterile.
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(II) Correct. Plasmodium, the causative agent of malaria, frequently changes its surface antigens to evade the immune response of the host, allowing it to persist.
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(III) Incorrect. Fasciola, or liver flukes, can cause a condition called "liver rot" in sheep, but it does not directly cause hypertrophy of red blood cells (RBCs). Instead, it affects the liver.
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(IV) Incorrect. Malaria is transmitted primarily by *Anopheles* mosquitoes, not *Culex* mosquitoes.