Good day!

I'd appreciate a hand with a few things here, whoever can spare some time.

Okay, the following were open ended sentences that I have completed in my workbook, as there are no answers given for open ended questions I need some help double-checking them....

1. Die jungen Eltern lieben ihr Mädchen sehr.

2. Können Sie bis zum Hauptmahlzeit bleiben?

3. Ich habe wirklich nichts gegen den Professor gesagt.

I do have a question about the accusative versus the nominative case. Can a sentence or phrase be both in the nominative and accusative case or does the nominative case cease to be when it becomes accusative?