# The energy of elastic waves is always:

1. Zero
2. Continuous
3. Quantized
4. Cannot be predicted

# The reciprocal of a reciprocal lattice is a —– lattice:

1. Normal
2. Direct
3. Reciprocal
4. None of the above

# The threshold generator is a:

1. Sine wave generator
2. Square wave generator
3. Saw-tooth wave generator
4. All of the above