填空题

1. Plants give out faint ______ when they are thirsty.	11
2. Many insects like to attack ______ plants.	12
3. To test his theory, Robert is using a device that can ______ plant cries.	13
4. A Healthy plant sounds ______ in Robert’s test.	14
5. The snapping pipes in plants make noises ten thousand times more quiet than a ______.	15