Which is an invention that improved safety for railway passengers? O refrigerated rail cars
O Pullman sleeping cars
O time standardization
O air brakes

Air brakes

Explanation:

D. air brakes is the correct answer.

Explanation:

to protect the united states' role as a world leader, president truman wanted to prevent the soviet union from spreading communism beyond its post-world war ii boundaries. he declared that the united states must assist any nations struggling to prevent a communist takeover.

- "bill clinton ( the 42nd u.s. president, served in office from by low unemployment, declining crime rates and a budget surplus. during clinton's second term, the u.s. economy was healthy, unemployment was low and the nation experienced a major technology boom and the rise of the internet."