In a relational database design, all relationships are expressed by . Creating a line between entity types Creating a primary key Creating a super key Creating a foreign key

"Creating a forign key" is the correct answer for the above question.

Explanation:

A relational database is used to hold the data. The data is stored in the cell which is made up of columns and rows and found in the table structure.This database uses the relational table to store the data. So there can be two types of table, primary table, and the secondary table. 'The secondary table holds the foreign key which maps the data from the primary table. The above question asked about the key, which is used to read the data of the relational table. This key is known as the foreign key. Hence this option is correct.While the other options are not correct because others are not used to read the data from the secondary table.

It's most likely choice a, it makes the most sense in my opinion.