Help: some plsql question

Which statement about multiple column subqueries is true?
A a pairwise comparison produces a cross product
B a nonpairwise comparison produces a cross product
C in a pairwise subquery, the values returned from the subquery are compared individually to the values in the outer query
D in a nopairwise subquery, the values returned from the subquery are compared as a group to the values in the outer query

which statement is valid about projection?
a) projection allows you to choose rows
b) projection allows you to choose columns
c) projection allows you to join tables
d) projection allows you to add colums to a table

19. which operator can not be used in nonequel join.
a. in.
b. like.
c. equal operator *
d. between...and..

49. which statement about implicit cursor is true?
a. implicit cursor are declared implicitly only for dml statement.
b. implicit cursor are dclared implicitly for dml statement and all select statement. *
c. programer need to close all the implicit cursor befor the end of pl/sql program.

45. which situation about implict cusor is true
a. all dml

b. all dml and select statements

i choice: b