What does "these" refer to

The authors use the word “backbone” in lines 3 and 39 to indicate that

When your working with the passage-based reading questions on the psat do all of the following except. a)make sure you read each question throughly. b) try to answer each question before you look at the answers. c) plan to spend most of your time reading the passage. d) make sure your answer choice is the most correct number me

To safely control the traffic flow and protect workers near public roadways and moving construction equipment use you could use