What is one of the most effective security tools available for protecting users from external threats?

it would be a. excessive network collisions or d. slow connectivity between devices those would be my answer.

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.