2. What is an echo? It is a compression wave that changes frequency in an unpredictable way.
It indicates the volume, or energy, of the sound.
It is a sound wave that vibrates in one direction towards a different source.
It is a sound wave that has been reflected, or bounced back, toward its source.

the major pests we deal with are insects, weeds and fungal diseases. a pesticide is a product, whether organic or chemical, used to kill the target pest. there are other techniques gardeners should use that can prevent the severe infestations that make the use of pesticides necessary

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explanation:

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