A network design shows that R1 has four different possible paths from itself to the Data Center subnets.
Which one of the following commands is most likely to show you all the possible next - hop IP addresses for these four possible routes?（）

You need to design a student registration database that contains several tables storing academic information.
The STUDENTS table stores information about a student. The STUDENT_GRADES table stores
information about the student's grades. Both of the tables have a column named STUDENT_ID. The STUDENT_ID column in the STUDENTS table is a primary key.
You need to create a foreign key on the STUDENT_ID column of the STUDENT_GRADES table that
points to the STUDENT_ID column of the STUDENTS table. Which statement creates the foreign key?（）