D. Por el uso de tubos de vacio.
Answer:
Stateful frame filtering
Explanation:
<h2><u>Fill in the blanks</u></h2>
A <u>Stateful frame filtering </u> keeps a record of the state of a connection between an internal computer and an external device and then makes decisions based on the connection as well as the conditions.
A composite primary key applies to more than one field. <span>A table can have only one primary key, which may consist of single or multiple fields.</span>
A composite primary key is selected from Design view. <span>In Design </span>view<span>, you can use the </span>Primary Key<span> button to assign or remove the </span>primary key<span> designation for the </span>selected<span> field or fields.</span>