Assertion (A): In triangle ABC, D lies on AB and E lies on AC with AD = 3.5 cm, DB = 5.6 cm, AE = 4.5 cm and EC = 7.2 cm; therefore DE is parallel to BC. Reason (R): The Basic Proportionality Theorem says that a line drawn parallel to one side of a triangle divides the other two sides in the same ratio. Choose the correct option.

A is true: $\frac{AD}{DB}=\frac{3.5}{5.6}=0.625$ and $\frac{AE}{EC}=\frac{4.5}{7.2}=0.625$, and equal ratios do force $DE$ to be parallel to $BC$. R is also a true statement — but it is BPT itself, which starts from a parallel line and deduces the ratio. A argues in the opposite direction, from equal ratios to a parallel line, and that needs the CONVERSE of BPT. A true reason pointing the wrong way is not an explanation, so the answer is that both are true but R does not explain A.