If evidence is described as incontrovertible, it is:

The term "incontrovertible" is defined as something that cannot be denied or disputed; it is absolute and beyond question. Therefore, when evidence is described as incontrovertible, it signifies that it is so strong and clear that it cannot be reasonably challenged.

This sense of certainty imbues the term with an implication of reliability and truth, which aligns perfectly with "unquestionable." Evidence that is incontrovertible is recognized widely as valid, making it credible in any argument or discussion.

On the other hand, the other options present a contrasting nature. "Conjectural" suggests something based on conjecture or hypothesis without solid proof, while "highly debated" indicates that the evidence in question is subject to disagreement or contention. Lastly, "weakly supported" implies that the evidence lacks strong backing, which directly contradicts the concept of being incontrovertible. Each of these alternatives highlights uncertainty or lack of robustness, unlike the clear and firm nature signified by "unquestionable."