Which code should you insert at line 03?

You are creating a console application named App1.
App1 retrieves data from the Internet by using JavaScript Object Notation (JSON).
You are developing the following code segment (line numbers are included for reference only):

You need to ensure that the code validates the JSON string.
Which code should you insert at line 03?
A. DataContractSerializer serializer = new DataContractSerializer();
B. var serializer = new DataContractSerializer();
C. XmlSerlalizer serializer = new XmlSerlalizer();
D. var serializer = new JavaScriptSerializer();