If you create a chart in Excel from data that will be frequently updated in Access, it is best to ________ the data

Based upon the contents of the ORDERS table in the accompanying figure, which of the following SQL statements will display all orders contained in the ORDERS table that have been shipped to the customer??

A) SELECT * FROM orders WHERE shipdate = 'NOT NULL'; B) SELECT * FROM orders WHERE shipdate = NOT NULL; C) SELECT * FROM orders WHERE shipdate IS NULL; D) SELECT * FROM orders WHERE shipdate IS NOT NULL;

The PDU at the Data Link layer is called a ____________.

Fill in the blank(s) with the appropriate word(s).