A white, cheesy substance that protects the fetal skin is

The category "animal" has a graded structure, which means that

a. most of the examples are well known to the general public. b. the members of that category are not all equally representative of that category. c. procedural knowledge is more important than declarative knowledge. d. there is a family resemblance among the members of this category.

Studies on stress and the immune system firmly suggest that

a. a sense of hope can reverse a terminal illness b. stress weakens the immune system, making us more susceptible to illness c. depression has little effect on the immune system d. the lack of sufficient "will power" is definitely a cause of cancer