Answer the true$/$false questions below, providing a brief explanation of your answers. You will not receive marks

for answers without explanation.

Relations that are in $3$NF must also be in BCNF$.()$ TRUE $()$ FALSE

The projection operation selects certains rows $($tuples$)$ of a relation. $(1$ TRUE $()$ FALSE

In SQL$,$ an attribute declared as UNIQUE can have NULL as its value. $()$ TRUE

$()$ FALSE

In SQL$,$ every table must have at least one candidate key. $()$ TRUE $()$ FALSE

A foreign key in a table R$,$ which refers to an attribute of another table S$,$ must not be null in R$.$

$()$ TRUE $()$ FALSE