Ican't get this wrong. these parts are made from pieces that are exactly the same:
a. interchangeable parts
b. steam engines
c. mass production
d. railroad ties

I gonna have to go with A. There's hundreds of different types of steam engines and mass production is simply the mass production and a good and railroad ties...it just didn't make sence to me because there are many different materials you can use that will serve as a railroad tie.

Taking a shower. why is cause as you shower the water is running more than taking a bath, washing a load of dishes or brushing your teeth. water is being used more by taking a shower and depending on how many people live in the household that take showers. some take a shower twice a day.