The notochord in vertebrates is modified into

Which one of the following features are true for chordates?
$(a)$ Heart is ventral.
$(b)$ Pharyngeal gill slits present.
$(c)$ Central nervous system is ventral,solid and single.
$(d)$ Post-anal tail is present.
$(e)$ Notochord is present.
Choose the most appropriate answer from the options given below:

Which of the following is a Cephalochordate?

Which of the following is not included in the phylum $Chordata$?

What do $a$ and $b$ represent in the given chart respectively?

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?