Remember: a or an agrees with the very next word, whatever that word is. Fill each gap, then look carefully at which word the article is actually sitting next to.
(a)Explorers discovered ___ ancient temple hidden in the jungle.(1)
(b)She found ___ tiny insect crawling on the branch.(1)
(c)He wore ___ old, torn hat during the storm.(1)
(d)They built ___ huge, wobbly den from fallen branches.(1)