Cross join

What will be the output of the following scripts?
DECLARE @Test1 TABLE(a INT)
DECLARE @Test2 TABLE(a INT)
INSERT INTO @Test1
SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION SELECT 4 UNION SELECT 5
INSERT INTO @Test2
SELECT a FROM @Test1
SELECT COUNT(*) FROM @Test1, @Test2

A. 5
B. 10
C. 25
D. An error will be occurred.

Answer:[C]
Highlight to find out the answer.