Which of the Following Sequences Reflects the Successive Brain Wave $\rightarrow$

Which of the following sequences reflects the successive brain wave patterns sleepers display as they fall asleep and enter progressively deeper sleep stages?

A) theta $\rightarrow$ alpha $\rightarrow$ delta
B) alpha $\rightarrow$ delta $\rightarrow$ theta
C) alpha $\rightarrow$ beta $\rightarrow$ theta
D) alpha $\rightarrow$ theta $\rightarrow$ delta