Which three are true about scalar subquery expressions?

A、A scalar subquery expression that returns zero rows evaluates to zoro
B、They cannot be used in the values clause of an insert statement*
C、They can be nested.
D、A scalar subquery expression that returns zero rows evaluates to null.
E、They cannot be used in group by clauses.
F、They can be used as default values for columns in a create table statement.