1. C – highly. This is the only adverb that collocates with ‘desirable’ here to convey the meaning ‘very or extremely desirable’. ‘Largely’ and ‘mostly’ have the meaning ‘more often than not’.
2. C – dates. To date back is to exist form some particular time in the past. To take back is another phrasal verb here, but the meaning is to take somebody in the past, figuratively.
3. B – with. ‘To associate with’ is to make a mental connection, e.g. ‘Expensive cars are often associated with wealth and speed’.
4. A – form. ‘In the form of’ means that money was one of the many ways to use gold. The word ‘way’ doesn’t fit though as it does not have this meaning in the given phrasing.
5. D – precious. Another collocation is ‘precious metal’. All the other adjectives work here, but ‘precious’ is the preferable choice.
6. C – application. ‘to find application’ means to discover a way to be useful. ‘to find purpose’ has the same meaning, but it is normally used in relation to people rather than inanimate objects.
7. A – properties. Property is the ability of something to do something. Conductive property is the ability to conduct electricity (pass electricity through one’s body). Most metals conduct electricity.
8. D – dishes. ‘Foods’ refers to different kind of food, e.g. bread, vegetables and so on. ‘Portions’ and ‘servings’ refer to the amount of food served.