Exercise 1:
an ocean
a pebble
an insect
a bug
a web
an archaeologist
an eagle
a geologist
a fossil
an ancient fossil
You only change "a" to "an" when the next word starts with a vowel.
Answer:
The topic sentence expresses the main idea of the paragraph combined with the writer’s attitude or opinion about the topic. Good topic sentences contain both a main idea and a controlling idea, are clear and easy to follow, use engaging vocabulary, and provide an accurate indication of what will follow in the rest of the paragraph.
Explanation: