Complete the alien's field notes about human belongings. Choose the correct phrase for each blank.

I sat on the hood of the car to observe the humans. Suddenly, I watched the two sisters' backpacks fall to the ground.

I sat on the hood of the car to observe the humans.

"Car" is an inanimate object, so we usually use the "of" phrase (the hood of the car) instead of an apostrophe.

Suddenly, I watched the two sisters' backpacks fall to the ground.

For a regular plural noun that ends in "s" (sisters), we only add an apostrophe at the very end to show possession.