Get Rdlc Data from two tables in c#

Question

Hello, I have two tables Reading (CODE, READING, TIMESTAMP) and Description (CODE, EXPLANATION) where CODE is primary key.

 

My report showing data like

 

CODE   |   READING   |   TIMESTAMP 

 

But I need to show the report like

 

CODE   |   READING   |   TIMESTAMP   |   EXPLANATION

 

What I do, I go to Report and press Ctrl+Alt+D (Report Data), add another DataSet but when I drag the Field from second DataSet the systems shows you just drag the fields from first DataSet.

 

Can anyone know how can I show what I need? Please help.

 

Advance thanks