Your thesis / topic sentence is true because it is grounded on facts. These facts will have to be supported by evidence. The evidence can come from reality. If this is the case, you will have to use some devices to gather information. Some of these can be carrying out interviews, taking pictures or video taping. This evidence will help you support your thesis. Then, you will give your reasons why you have stated the thesis and you will also have to back this up with other authors' opinions.
The ghost of Christmas yet to come has the most impact on Scrooge because it makes him fear what has yet to come and makes him want to change in any way possible.