Answer: Caused to be a certain nature
Explanation:
If you replace the word “rendered” with “caused to be” the statement still makes sense. A good rephrasing would be:
The sad cries of the many slaves, horrible yesterday, are made worse by the joyous shouts that they hear.
I don't think a correction is necessary. Both parts of the sentence are already in the present tense. Plus, the use of "us" in the beginning of the sentence indicates a personal attachment.
Answer:
Yes it is possible
You are correct.
to conduct an experiment
