Read the following sentences:

I always get the vaccine. I haven't gotten the flu in years.

Which revision below is a complex sentence?

○ The reason why I haven't gotten the flu in years is because I always get the vaccine.

○ I always get the vaccine; thus, I haven't gotten the flu in years.

O I always get the vaccine, which means I haven't gotten the flu in years.

O I always get the vaccine, so I haven't gotten the flu in years.​