Concept:A compound adjective formed with a number and a noun must be hyphenated and singular when it comes before another noun.
Explanation:The word needed describes the noun "panel".
When "seven" and "man" are joined to modify "panel", they act as one single adjective.
Such number-plus-noun compounds are written with a hyphen: "seven-man".
The noun in the compound stays singular because it is part of an adjective, not a plural noun.
Therefore, "seven-men" and "seven men" are incorrect in this position.
"Seven man" is also wrong because it has no hyphen.
Thus the correct completion is "seven-man panel".
Answer:D. seven-man