·1832 cyrus mccormick develops the mechanical reaper · 1837 john deere patents the steel plow · 1892 john froelich builds the first gasoline-powered tractor · 1895 refrigertion techniques developed in the u. s. which sector of the american economy would have been impacted most by the developments listed in this timeline? a) the energy sector b) the industrial sector c) the agricultural sector d) the communications sector

Ah, this is simple
What do all of these inventions have in common? Well, let's see.
The Mechanical Reaper, developed by Cyrus McCormick, is used to harvest crops mechanically.
The Steel Plow, patented by John Deere, is used to break apart tough soil, to easily plant crops.
The gasoline-powered tractor, built by John Frolich, is used for a number of things, but all to do with farming.
The Refrigeration techniques...This is for food preservation. 

The thing they all have in common is all of these developments have a purpose in agriculture. Crops, Crops, more Crops, and Preserving harvested Crops. 
Your answer is these developments would have most heavily impacted the agricultural sector, C

~Hope this helps!