Answer: The answer is (a) Timeline.
Step-by-step explanation: Given that Alex wants to synthesise information regarding when the books were written.
The option are to create a timeline, a Venn-diagram or a chart.
Out of these, I think the best option is to create a timeline, where Alex can easily display the list of books along with the time in a particular order , so that it will be easy for others to read and understand.
Venn-diagrams and Charts will not serve Alex's purpose here.
Thus, the correct option is (a) Timeline.