When sound passes from one medium to another where its propagation speed is different, which of these change: frequency, wavelength, speed?

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?

Why does bubbling occur when vinegar mixed with baking soda

What are the student's observations and inferences before he starts his investigation?