1. Wherever icebergs are present, threats to shipping exist. Icebergs are not present in the South Pacific. Hence, there are no threats to shipping in the South Pacific.

2. According to surveys, there are college students who think that Africa is in North America. But anyone who thinks that has no knowledge of geography. It follows that there are college students who have no knowledge of geography.

13. Diseases carried by recessive genes can be inherited by offspring of two carriers. Thus, since cystic fibrosis is a disease carried by recessive genes, it can be inherited by offspring of two carriers.

4. All of the movies except the romantic comedies were exciting. Hence, the action films were exciting, because none of them is a romantic comedies.

5. Autistic children are occasionally helped by aversion therapy. But aversion therapy is sometimes inhumane. Thus, autistic children are sometimes helped by inhumane therapy.

Translate the following arguments into standard-form categorical syllogisms, then use Venn diagrams or the rules for syllogisms to determine whether each is valid or invalid. See Section 4.7 for help with the translation.