Read the following statements.

Assertion (A) : Amphioxus is placed under the subphylum Cephalochordata

Reason (R) : Notochord is confined only to the head region in Amphioxus.

• A

  Both A and R are true and R explains A

• B

  Both A and R are true and R does not explain A.

• C

  A is true, but R is false

• D

  A is false, but R is true