Which phrase best describes the situation about traffic delays?

The phrase "were probably held" accurately conveys a sense of uncertainty about the traffic delays while suggesting a strong likelihood that they occurred. This indicates that there is reasonable evidence or indications leading to the conclusion that delays did happen, but the degree of certainty is not absolute.

In contrast, the other options lack the same balance of likelihood and tentativeness. For example, "were likely to be held" implies potential future delays rather than past ones, which doesn't fit the context. "Were certainly delayed" presents a definitive assertion, which does not account for any uncertainties or variations that might have caused the traffic situation. Meanwhile, "were possibly held" is too vague and weak, lacking the degree of assurance needed to accurately describe that delays were likely.

By choosing "were probably held," it captures the expected situation about traffic delays, reflecting the nuances involved when discussing such outcomes in a more factual narrative.