Which expression indicates Bruce was very surprised about his promotion?

The expression "He could have been knocked down with a feather" vividly conveys the sense of extreme surprise or astonishment. This phrase suggests that Bruce's surprise was so profound that even something as light as a feather could have affected him dramatically. It implies that his reaction to the promotion was unexpected and left him in a state of disbelief or overwhelming emotion. This type of figurative language effectively illustrates the intensity of his surprise, making it a clear choice to indicate his reaction to the news.

The other expressions provided do not convey surprise effectively. For instance, "He expected it" suggests that Bruce anticipated the promotion, which negates any feelings of surprise. Similarly, "He was underwhelmed" implies a lack of excitement or disappointment rather than surprise. The phrase "He was shocked" does suggest surprise, but it lacks the vivid, illustrative quality of the chosen expression, making it less impactful in conveying the depth of Bruce's emotion.