When a program lets the user know that an invalid choice has been made, this is known as: ?

When a program lets the user know that an invalid choice has been made, this is known as a error message.

solution:

the right option is a

to adding   a new row to a table we   have to do process last table cell and pressing tab.

this is the process to add new row in the cell:

* to add a row below the cell, click insert below in the rows and columns group.

thus this is the required right answer.