Sometimes, when it's dark at night, i see people in the dark corner of a room, and they just stare back at me, or wave, then i'll blink and they'll go away, or not be there anymore. is something wrong with me.

What link in the chain of transmission is described in the paragraph? sarah has been eating and sleeping poorly. she was just diagnosed with pneumonia. tests showed the illness was caused by streptococcus pneumoniae. in the chain of transmission, sarah is the (blank) , and streptococcus pneumonia is the (blank).