Which innovations of the second industrial revolution improved a technology of the first industrial revolution and thereby contributed to expanding industrial growth?
a. iron replaced steel and made bridges and buildings safer and longer lasting, thus reducing maintenance costs.
b. radio replaced the telephone and thus made personal communications less costly.
c. by improving the steam engines powering ships, the capacity of sea-going vessels increased.
d. by replacing steam, electricity enabled artificial lighting, which expanded factory work hours and production.