One of the primary characters of chordates is

Which of the following features is present in all chordates at some stage of their life?

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 $Cephalochordata$.

Mode of feeding in tunicates is

What is the classification of the subphylum $Vertebrata$?

In which of the following is the $rotatory$ $organ$ (wheel organ) found?