Select from options: Continue writing the next sentence.

How to choose a heartworm preventative for your cat
Have your cat tested for heartworm.
Even before you begin looking for a heartworm preventative, you should take your cat into your veterinarian's office and have the animal tested for heartworm. It would be deeply unfortunate to begin giving your cat preventative medication, only to find that it already has heartworm.

OPTIONS:
(I). If the test results come back positive, you can speak with your vet about how to treat the heartworm. Talk to your vet about preventative heartworm medications..
(II). Be sure to always check the information the vet writes on your cat's prescription. Ask your veterinarian to test your cat for heartworm preventative medication..
(III). Heartworm preventative medicines are available at pet supply stores. You will typically need to set up a second appointment with your veterinarian or call your local poison control center for advice..
(IV). To ensure that there is no existing heartworm, you need to look for an appropriate, safe brand of heartworm preventative. A reputable brand is one that shows up on the vet's office cabinet..
Answer:
(I).