Which of the following is a distinct character of the phylum Chordata?

Label the parts $P$,$Q$,$R$,and $S$ in the given diagram of a chordate:

Which one of the following structures is present in all adult vertebrates?

Statement-$1$ : Cephalochordata bears notochord all along the body throughout life.
Statement-$2$ : Urochordate bears vertebral column only in tail region throughout the life.
Then which is correct?

The beak in birds is toothed in

Assertion : Acraniata is a group of organisms which do not have a distinct cranium.
Reason : It includes small marine forms without a head.