$6.$ Given the list manipulation below, what will list$1$ contain after execution?

list$1=[\text{'}$a$\text{'},\text{'}$b$\text{'},\text{'}$c$\text{'},\text{'}$d$\text{'}]$

list$2=$ list$1[$:$]$

list$2[1]=\text{'}$x$\text{'}$

A$)[\text{'}$a$\text{'},\text{'}$x$\text{'},\text{'}$c$\text{'},\text{'}$d$\text{'}]$

B$)[\text{'}$a$\text{'},\text{'}$b$\text{'},\text{'}$c$\text{'},\text{'}$d$\text{'}]$

C$)[\text{'}$a$\text{'},\text{'}$b$\text{'},\text{'}$x$\text{'},\text{'}$d$\text{'}]$

D$)[\text{'}$a$\text{'},\text{'}$b$\text{'},\text{'}$c$\text{'},\text{'}$x$\text{'}]$