A. Hershey-Chase experiment: DNA of S bacteria caused R bacteria transformed (iv).
B. Replacing uracil with thymine: DNA as genetic material (i).
C. Avery, MacLeod and McCarty work: DNA gets stability (ii).
D. Plane of one base pair stacks over other: Stability to helical structure (iii).
Final Answer:
A-iv, B-i, C-ii, D-iii