The following two datasets are joined on CustomerID. What is the cause of the $$String fields can only be joined to other string fields$$ error message received when joining the datasets?

Input $1$: Input $2$:

Error:

A$.$

One CustomerID field has more records than the other.

B$.$

The DateofLastVisit and Spend fields are not strings.

C$.$

The two tables have different second fields.

D$.$

One CustomerID field has leading zeroes.