First decide which of the following nouns best completes the first blank in the following pairs of sentences. The same noun will be used for each sentence in the pair. Then decide if both that and which can be used in the second blank, or if only that is possible. What does this tell us about the difference between a relative clause and an appositive clause?

suggestion; impression; discovery; knowledge; fear

1. (a) The _______ _______ fire could be harnessed and tamed was a turning point in the history of our species.

(b) The _______ _______ these scientists have made far exceeds the initial goals of the investigation.

2. (a) A phobia is an irrational _______ _______ causes the person suffering from it to avoid the feared object or situation.

(b) The _______ _______ others might be having positive experiences from which one is absent has been accentuated by the use of social media.

3. (a) I’d like to discuss the _______ _______ I made at last month’s meeting, since it seemed at that time to generate some interest.

(b) The _______ _______ I might somehow be involved in the scandal is nothing less than preposterous.

4. (a) The _______ _______ we are mortal is something that some people find terrifying, whereas others feel it helps to relativize.

(b) The _______ _______ we are currently gaining in this area will have long-term ramifications on how the disease is treated.

5. (a) Do you ever get the _______ _______ you’re falling when you slip into the state of sleep?

(b) The _______ _______ you make on someone the first time you meet them is likely to stay with them for a very long time.