A shipping company that operates cargo ships traveling between which pair of port cities would have benefited the most from the construction of the Panama Canal.
A. Los Angeles and Miami
B. Miami and Huston
C. New York and Miami
D. Seattle and Los Angeles

Explanation:

I have attached two pictures.

First picture shows the location of Seattle, Los Angeles, Houston, Miami, and New York on the map of the United States.

I have added a red circle around each of those cities to permit you to find them easily.

Second picture shows the location of Panama Canal in Central America, in relation to the United States. I also added a red circle to help you.

From the first picture, you can see:

        Look at the second picture, now: Panama Canal permits that vessels travel between the East Coast and West Coast through sea: passing from Pacific Ocean (West Coast) to Atlantic Ocean (East Coast) and viceversa.

That is the importance of Panama Canal: it connects Pacific Ocean and Atlantic Ocean.

i think the answer to your question is: settlement of the interior and economic growth. ( ^_^)／