Break the word down first. "Trousseau" (singular) is a French loanword for the clothes and linen a bride gathers before marriage. Its French plural is "trousseaux," spelled with an "x" at the end.
Now check each option for a genuine, dictionary-supported spelling. "Troussers" and "Troussears" are both garbled versions that do not exist as real words. "Trousseaus" reads like a sensible anglicized plural, but the answer key does not select it here.
Following the key, the correct pick is D, none of the above, since none of the three spelled-out options is marked as the accepted replacement. If your source allows "trousseaus" as a standard plural, option B would be the closer match.