The prefix anti- means against. So an "antidote" is something used against poisons, used to provide a solution to poison. This is closest in meaning to "medicine." 

To solve this synonym you need to rely on your knowledge of prefixes. The prefix du- means two of, so a "duplicate" is a second copy of something. It is common to make a "duplicate" of something if it is important and you do not want to lose it, like a "duplicate" key. 

To solve this synonym you will again need to rely on your knowledge of prefixes. The prefix dis- means away. So to "dispatch" something is to send it away. To provide further help, "lent" means let someone borrow. 

The prefix pre- means before, so "prevent" means to stop something before it happens. To provide further help, "accompany" means go with; "continue" means keep going; "dispatch" means send away; "displace" means replace, take over.

The prefix sub- means under. Someone who is "submissive" is someone who likes to be controlled by someone else, someone under control. The closest word to this is "obedient" which means someone who does what they are told. To provide further help, "hostile" means not friendly, threatening; "dominant" means in-charge, it is opposite in meaning to "submissive"; "frenetic" means chaotic and fast-paced; "unusual" means weird, not normal.

The prefix mal- means bad so you can reasonably infer that the correct answer must mean something bad. Something that is "malignant" is deadly, bad for you and dangerous. To provide further help, "benign" means not malignant, not deadly, harmless; "unkempt" means messy; "scarce" means rare, in short supply. 

The prefix proto- means first. So, a "prototype" is an early or first model of something. Additionally, "elementary" means basic, not complicated. 

The prefixes dys- and dis- means not. As in "dislike" which means to not like. Furthermore, "functional" means working properly. So, "dysfunctional" means not working. This is closest in definition to "broken." Additionally, "precious" means treasured, very special and important to; "literate" means able to read and write; "plucky" means courageous, brave, usually it describes someone small who is braver than might be expected; "repaired" means fixed.

The prefix morph- means shape. So, to "morph" literally means to change shape. Additionally, "suffer" means feel pain; "rejoice" means celebrate, draw happiness from; "unite" means bring together, join, connect; "preach" means deliver a speech to a group of people, particularly a religious message. 

The prefixes con-, and com- mean with, together. As in "convene," which means meet, come together to discuss. So, "compact" means something like pushed together or "dense." If you need further help, "dense" means thick, tightly packed together.