Select the most appropriate option to fill in blank number 1.
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. backbones.
The passage talks about the life process. As the passage starts with a plural subject, so filler 1 should also take a plural form of the word. So, the word backbones will fit the sentence correctly which means the row of small bones that are connected together down the middle of your back.