1. This candle will keep the room

bright.

2. This candlelight will keep the room
bright.

Can both be used? Which one is frequently used?)

3. We breathe with our noses.
4. We breathe through our noses.
(Are both OK?)

5. We could not go on a picnic because of rain.

6. Rain prevented us from going on a picnic.

(Are both the same? And can we use 'thanks to' instead of 'because of'?))

7. He kept on running.
8. He kept running.

(What is the difference between them?)

1 is better than 2; #2 has the word "light" repeated unnecessarily.

4 is better than 3.

5 and 6 are saying the same thing. Yes, you can use the expression "thanks to" instead of "because of" -- it's rather sardonic!
http://www.answers.com/sardonic

There is little difference between 7 and 8. They are saying the same thing.

With 1 and 2, "candle" indicates one candle, while "candlelight" can be coming from multiple candles.

I hope this helps a little more. Thanks for asking.

1. Both sentences are grammatically correct and can be used to convey the same meaning. However, the first sentence "This candle will keep the room bright" is more frequently used in everyday language.

2. Similarly, both sentences "We breathe with our noses" and "We breathe through our noses" are grammatically correct and convey the same meaning. However, the second sentence "We breathe through our noses" is more commonly used.

3. The sentences "We could not go on a picnic because of rain" and "Rain prevented us from going on a picnic" have a slightly different emphasis. The first sentence emphasizes the reason for not being able to go on a picnic (the rain), while the second sentence emphasizes the outcome or result of the rain (prevented us from going). Both sentences are correct, and you can use "thanks to" instead of "because of" to convey a similar meaning: "We could not go on a picnic thanks to the rain."

4. The sentences "He kept on running" and "He kept running" have a subtle difference. "He kept on running" suggests continuous or repetitive action, emphasizing the ongoing nature of the activity. On the other hand, "He kept running" implies he maintained the activity of running without interruption. Both sentences are correct and convey similar meanings, but the choice depends on the desired emphasis or context.