1. Madrigals are old songs (16/17th century). So I'd go for answer (a), pastoral songs.
2. This question does not read correctly. A millennium is a period of a thousand years.
3. A mortgage is actually a form of security granted over property involving the transfer of ownership. The closest answer is (b), pawned, although they are not technically synonymous.
4. Nominal means "in name only". (d) is the best answer as "ostensible" means "apparent".
5. A prig is someone who is self-righteously moralistic. So answer (a) would fit best.
6. A sanction is a threatened penalty. So (b) is the closest.
7. A snarl is a growl with teeth bared (this word is an example of onomatopoeia - word formed from the sound with which it is associated). So, answer (d).
A good resource for words is the online OED http://www.askoxford.com/dictionaries/?view=uk