For the $1-1$ relationship rule, which of the following statements is not correct?

Group of answer choices

If one side is mandatory, one side is optional, use primary key of the parent entity in the dependent entity as foreign key.

If the two entities are kept separated when both sides are mandatory, It does not matter which primary key you select as foreign key in another entity.

Entities can be amalgamated when both sides are optional.

The general rule is to select the design which cause the fewest nulls.