Which of the Following Statements Is Not Deductively Valid

Multiple Choice

Which of the following statements is not deductively valid?

A) If people watch television,then they get a headache.They watch television.
Therefore,they get a headache.
B) If a student writes an abstract for a paper,then she gets a good grade.A student's paper is abstract.Therefore,the student gets a good grade.
C) If the sky is clear,then there are no clouds.The sky is clear.Therefore,there are no clouds.
D) If a black cat crosses your path,then you will have bad luck.A black cat crosses your path.Therefore,you will have bad luck.