Answer: In the sentence "When packing the order yesterday, one important item was omitted", there is a B. dangler.
Explanation: A dangling modifier or dangler is a sentence element that is not modifying the correct noun or pronoun. In other words, a dangling modifier does not modify the intended subject. In the sentence "When packing the order yesterday, one important item was omitted", "when packing the order yesterday" is erroneously modifying the noun phrase "one important item". Since an item cannot pack an order, the sentence can be corrected by writing "When packing the order yesterday, I omitted an important item".