In a data dictionary, the column marked as the key is the one that:

Answer

Is unique per record and is never summed or averaged

Options - A. Is unique per record and is never summed or averaged - B. Is always numeric, so that it can be sorted quickly - C. Appears first in the header row of the sheet - D. Holds the largest number of distinct values in the table Why - A. Correct — the key identifies the record. It is what a merge matches on and it is never a quantity. - B. Keys are often digits but are categorical identifiers; a text key such as "A100" is just as valid. - C. Position is a convention, not a property. A key can sit anywhere in the header. - D. Uniqueness is the property, not variety: a key has exactly one row per value, which is stronger than "many values".