In the early 1800s, mass production was made possible by
a. the use of interchangeable parts.
b. the use of handmade products.
c. the use of skilled laborers.
d. the use of expensive materials.

c) The use of skilled laborers

Explanation:

I answered this question and got it right

c holding free elections

the  seven  days  battles  were  a series of seven battles over seven  days from june 25 to july 1, 1862, near richmond, virginia,  during  the american civil war. the  seven  days ended with mcclellan's army in relative safety next to the james river, having suffered almost 16,000 casualtiesduring  the retreat.