Fairly sure we go to the same hs but I put A. It might be c though. Not totally sure.
4.6 billion years ago - most likely hydrogen (H2) and helium (He)
probably rich in hydrogen compounds like methane (CH4), ammonia (NH3), hydrogen cyanide (HCN), water (H2O), and formaldehyde (HCHO). Also some N2, CO2 but LITTLE or NO free oxygen.
Molecules of H2 and He move really fast, especially when warm, that they eventually all escaped Earth's gravity and drifted off into space.
Answer:
Hey!
Your answers are...
Algeria, Burkina Faso, Mali, Sierra Leone, Mauritania, Liberia, Côté D'Ivoire, Morocco, Western Sahara, Senegal, Guinea
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It is impossible to build a drainage system on the outside of the Sao Francisco river as buildings are built on the outside of the foundation.
The Subarnarekha is developing a small drainage system.
The Amazon basin is the largest drainage basin in the world.
The Urugay drainage system includes the greater part of southeastern Brazil, Paraguay, southeastern Bolivia and northern Argentina
So i would suggest putting the Amazon as it is the most common known and largest. Remember to use geographical terms!