The given figure shows a solid formed using two puzzle pieces. Which of the following are the two puzzles pieces?
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, R and S (d) P, Q, R and S