Fill in the numbered blank (iv).

Directions: Choose the best option to fill in the blank.

Yawning is an involuntary ______(i)______ in which your mouth opens up wide and you inhale deeply, followed by _____(ii)_____. When you say involuntary, this means that you have no _____(iii)_____ over this action much like other reflexes such as blinking or sneezing. Yawns are not _____(iv)______ only to human beings as all other animals do this. Despite a lot of _____(v)_____, we still know little about the causes of yawning.