It should be "Linking" word
Answer:
<u>1</u><u>)</u><u>Amplitude</u>
<u>2</u><u>)</u><u>Modulation</u>
<u>3</u><u>)</u><u>Frequency</u><u> </u>
<u>4</u><u>)</u><u>Modulation</u>
Answer:
What Happened? Which Characters caused it to happen?
Explanation:
That is my best guess.