Which of the following is another characteristic of animals possessing a solid nerve cord?

Urochordata: All the members of this subphylum are:

Which of the following statements are true for the phylum $Chordata$?
$(a)$ In $Urochordata$,the notochord extends from head to tail and is present throughout their life.
$(b)$ In $Vertebrata$,the notochord is present during the embryonic period only.
$(c)$ The central nervous system is dorsal and hollow.
$(d)$ $Chordata$ is divided into $3$ subphyla: $Hemichordata$,$Tunicata$,and $Cephalochordata$.

Assertion $A$: $Amphioxus$ is not a vertebrate.
Reason $R$: $Amphioxus$ is not a chordate.
Which option is correct for Assertion $A$ and Reason $R$?

What is present in the larval stage of Urochordata?

All chordates at one or the other stage possess