I think so it ans wold be d.because if the source approaches the observer more and more wavefront will pass and it get squeezed.so wavelength decreases and frequency increases.
<span>Tectonic plates move because they are floating on top of the liquid mantle. The mantle itself moves due to convection currents: hot rock rises, gives off some heat, then falls. This creates vast swirls of moving liquid rock under the crust of the earth, which jostles the plates of crust on top.
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Answer: The FBI used a technique which is called Latent Fingerprint Identification: a silver nitrate solution was used to cause a reaction of the unseen fingerprints perspiration left by the kidnappers all over the ransom notes. The reaction caused the perspiration to turn into silver chloride. This substance is white and it is also visible to the naked eye which means the fingerprints of the perpetrators were easily identifiable.
sorry if this is wrong, i hope i helped
