Which of the following organisms possesses a notochord that extends from head to tail throughout its entire life?

One of the primary characters of chordates is

Which of the following is present during some stage of the life cycle in animals belonging to the phylum $Chordata$?

The most important distinctive character of $Chordata$ is the presence of

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

Identify the correct statement regarding Chordates.