Option B. The invention of the balance made trade easier. Increased trade contributed to the development of more complex writing systems.
Explanation:
Taking into account a cause-effect relationship that describes the development of both balance and writing is needed, one can immediately discern that both options B and D include the development of writing systems as effects for the causes provided.
However, option B makes a more appropiate presentation for the relationship, given the variation at the beginning of the second sentence compared to the first one, whereas option D uses "Increased agricultural production" for both ending the first sentence and starting the second one.
