Paraguay and uruguay are similar in many ways except in their a) large number of people living in cities b) export of cash crops c) past political repression d) use of the río de la plata

D) use of the Rio de la Plata

Explanation:

Uraguay and Paraguay are two nations located in South America, and they have lot of similarities between them. One big difference though is that Uruguay is coming out on ocean waters, while Paraguay is landlocked. Uruguay uses the Rio de la Plata as the most important place for its ports, thus for trading globally, while Paraguay is not able to do so as it doesn't have access to the Rio de la Plata.

they use tree rings to figure out weather patters.