You did not include options in your question, but based on the meaning of the word cryptic, your answer will be 'A HIDDEN MEANING'. When you say that something is cryptic, it means that, that thing has a meaning that is mysterious or obscure. From the way the word was used in the given sentence, it means that the message the teacher was passing across about the test is hidden, it was not understood by any of the students.
it would not be a good idea because dinosaurs are very powerful creatures and would kill every human in sight. dinosaurs could not be used for a lot of things unless you can tame/domesticate them.
