Humans use lots of water.
Hello. You did not enter the text to which this question refers, which makes it very difficult to answer it exactly. However, I will try to help you in the best possible way.
As you showed that the word "author" in line 10 was used as a proper noun, we can consider that the same word in line 4 was used in a general way and did not specify an exact person. This is because proper nouns are terms used to specify something or someone, as the question states that the word "author" was not used with the same meaning in line 4, we can consider that this is the difference.
The Nile river had a big impact on trade because it served as a source of transportation. Communities formed along the Nile were more developed.
Salt from the desert was a reliable and profitable resource traded.
Savannas were used to grow crops and the excess from the crops were traded.
