Which of the following is a characteristic of concrete operational thinking?
a. the ability to have complex abstract thought
b. the ability to understand conservation of matter
c. the ability to sort items by one characteristic only
d. the ability to formulate hypotheses or guesses

Which statement contains an opinion? the ants serve to protect the acacia from other plants and herbivores. the acacia depends on pollinators for the exchange of genetic material. the acacia has no chemical defenses to discourage herbivores. the ants provide the acacia with the best protection from other plants and herbivores.