1. They drilled through several layers of rock to reach the oil.

2. They drilled through several layers of a rock to reach the oil.

3. They drilled through several layers of rocks to reach the oil.
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Which one is right? Do we have to use 'rock,' 'a rock,' or 'rocks.'

1 answer

The first one is right. Possibly the third, but not the second.

The first is really the best.