A Planaria worm is cut horizontally in the middle into two halves P and Q such that the part P contains the whole head of the worm. Another Planaria worm is cut vertically into two• halves R and S in such a way that both the cut pieces R and S contain half head each. Which of the cut pieces of the two Planaria worms could regenerate to form the complete respective worms ?
A. only P
B. only R and S
C. P, Rand S
D. P, Q, R and S
If the body of planaria is cut into any number of pieces, each piece grows into a complete organism through the process of regeneration.