Declaration of Independence

Chris: It was right then that I started thinking about Thomas Jefferson...the Declaration of Independence. And the part about our right to life, liberty and the pursuit of happiness. And I remember thinking: How did he know to put the "pursuit" part in there? That maybe happiness is something that we can only pursue. And maybe we can actually never have it...no matter what. How did he know that? 

It is … that/who … 

• It is from the sun that we get light and heat.
• It was not until I had read your letter that I understood the true state of the affair.
• 
  

My father did the experiment in the lab yesterday evening.

• 1. It was my father who did the experiment in the lab yesterday evening.
• 2. It was the experiment that my father did in the lab yesterday evening.
• 3. It was yesterday evening that my father did the experiment in the lab.
• 4. It was in the lab that my father did the experiment yesterday evening.