Which of the following is the correct output from this sequence of statements?

letters $=[\text{'}$a$\text{'},\text{'}$b$\text{'},[\text{'}$c$\text{'},\text{'}$d$\text{'},[\text{'}$e$\text{'},\text{'}$f$\text{'}]],\text{'}$g$\text{'}]$

print$($len$($letters$[2]))$