What is the location and function of the nerve cord in chordates?

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A):$ All vertebrates are chordates but all chordates are not vertebrates.
Reason $(R):$ The members of subphylum Vertebrata possess a notochord during the embryonic period; the notochord is replaced by a cartilaginous or bony vertebral column in adults.
In the light of the above statements,choose the correct answer from the options given below:

Which of the following animals has a closed circulatory system?

Which of the following is $NOT$ included in Protochordata?

The body of a urochordate is enclosed in a

Which of the following is the smallest taxonomic group of animals having a cranium,vertebral column,ventral heart,pulmonary respiration,and two pairs of limbs?