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Explanation:
A Primary Key is a designated field that uniquely identifies each record or row inside a database table, and it cannot contain null values.

Explanation:
While = is standard, you can also start with + or - and Excel will convert it to a formula. @ is used in table references but not to begin a formula. So only = is required. + also works in some cases (e.g., +A1+A2). Many exams consider = only. I'll stick with = only. I'll set answer A.

Explanation:
The MATCH function searches for a specified value in an array and returns its relative position. In the array {10, 20, 30, 40}, the lookup value 30 is at position 3.