Answer:
Amelioration is a process in which the meaning of a word is upgraded - a word with a negative connotation develops a positive connotation. Pejoration is a process that goes the other way round (from a positive to a negative meaning). It is clear that these are not the options in this example.
It is now important to determine whether the trend goes from a general meaning to a more specified meaning, or the other way round. The trend is: something returned -> income -> income from rent, so the answer is specialization.
