Omar observes that many buildings in his city were built using limestone. He has read that acid rain can damage limestone. He also knows that limestone reacts with acids and that chemical reactions are affected by temperature. With this in mind, he conducts an investigation to see how the amount of damage to the limestone is affected by the amount of acid on the stone. Which statement describes the correct plan for his procedure?

The temperature and the amount of damage to the limestone are controls. The amount of acid and the type of limestone are variables.
The temperature and the type of limestone are controls. The amount of acid and the amount of damage to the limestone are variables.
The amount of acid and the type of limestone are controls. The temperature and the amount of damage to the limestone are variables.
The amount of acid and the amount of damage to the limestone are controls. The type of limestone and temperature are variables.

can you show me the drop down menu? ill answer it after you've done that. ill edit this i mean promise

explanation:

in the door-way, with his head in the room and with a lantern in hand with the most slight ray of light shining from it; so small and opening it so slowly to not disturb the old mans sleep.

i have watched the play of this story last friday.

marian anderson was the first black aamerican to appear there. she played the role of ulrica in "a masked ball". anderson's appearance was mostly   symbolic, she was already past her prime as a singer, and she had made her succcess on the concert stage. in her first performance, she received a ten minutes ovation. the moment was considered momentous enough at the time to warrant a front page at the new york times story.

the singer wore an iridescent peasant blouse adorned with several beaded necklaces. the lights illuminated her features   from below, creating an aura of mysticism and darkening her expression in shadow. then, marian sang. when she hit the “a” note, she held it, and i knew that all   doubts about her skill must have melted away with that note.