"I think that I am being followed by a rhinoceros."
Translation:Ik denk dat ik door een neushoorn gevolgd word.
well... you're being followed by the rhino, so the rhino is the subject for "gevolgd wordT" google "dat ik gevolgd word" and see the results ;) I can't explain why (because i'm not a teacher) but in this case it's DT (i'm native dutch)
That is wrong as this phrase is in the passive voice. The verb in the phrase is "am/is being followed" and as you can see it is "I" that is being followed, not "a rhino". Therefore "I" is the subject and "word" is correct.
Change the word order, without changing the meaning of the sentence. It'll become 'Ik word door een neushoorn gevolgd[, denk ik]'. Here you can clearly see that 'ik' is the subject, while 'een neushoorn' is the object.
(I have googled "dat ik gevolgd word", and I do not see result with "dat ik gevolgd wordt"; so I do not see your point?)
(I am also a native Dutch woman)
"Ik denk dat door een neushoorn ik word bevolgd" was marked wrong. Is the word order sufficiently bad that the sentence is incorrect as I wrote it?