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 only during the embryonic period
(c) The central nervous system is dorsal and hollow
(d) Chordata is divided into three subphyla: Hemichordata, Tunicata and Cephalochordata