The host and the are always in this intimate dance together." Can someone help fill in the blank. Thank you xx

Name the following: (a) category of pathogen that causes diseases, like common cold and mumps. (b) the microorganism that requires a host to produce.

Ineed to know why d is the correct answer asap

What can be said about farmers in highly developed countries? a) they have little or no negative impact on the environment. b) they practice subsistence agriculture. c) they are able to incorporate polyculture into their farming practices. d) they utilize organic farming techniques on a regular basis. e) they rely on large amounts of energy from fossil fuels.