Will give brainliest! Which statement is TRUE?

1)Light waves always travel at a constant speed, but sound waves do not.

2)Waves travel at different speeds through different materials.

3)Wave speed depends on the amplitude of the wave.

4)Light waves and sound waves travel at the same constant speed.

Sea stars, sea urchins, sand dollars, and brittle stars are all memeber of a group, what is the common name of the group they are all in

Recent research by marine biologists suggests that bottlenose dolphins have names for themselves. scientists played sounds they had identified as the names of particular dolphins, putting them through a synthesizer so that they did not sound like the voices of particular dolphins. the researchers found that dolphins would respond to the names of other dolphins that they were related to or associated with, but they ignored the names of strangers. this discovery suggests a much greater degree of self-awareness in aquatic mammals than was previously suspected. if this research holds up, what does it suggest about dolphins?

Is there any species that went extinct in recent years due to natural causes (not caused by human interaction). if so, what caused it?