France was smart enough to see that Germany was isolating them, so they teamed with Great Britain and Russia (the triple entente). The outbreak of WWI started with the assassination of Archduke Franz Ferdinand of Austria by Gavrilo Princip of Serbia. Serbia for a long time had been asking for Independence, but Austria would not grant it to them, so Princip assassinated their beloved Archduke, which caused Austria to declare war on Serbia. Concerned that their close trading partner was going to collapse in a war, Russia got involved to protect Serbia. In order to protect Austria-Hungary, Germany stepped in to declare war on Russia. At this point the alliance system began to unfold as each country vowed to come to each other's assistance in the event of war.
I know you only asked about Germany's attempt to isolate France and how it was unsuccessful, but I wanted to provide information on the significance of France's counter leading up to WWI. Hope this was overly helpful! :)
"<span>B. Byzantine cities were excellent marketplaces for merchants from Europe, Africa, and Asia" is the only option that is completely true, although they did benefit from the silk trade. </span>