Which is true about a pure substance? A. An element is a pure substance because its melting point decreases when its mass decreases.

B. A compound is a pure substance because it has a single chemical composition.

C. A mixture is a pure substance because its parts can be visibly identified.

D. A solid is a pure substance because it has a higher density than a liquid.

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?

Ivan is looking at a cross section of a stem taken from a vascular plant. he sees two different types of vascular tissue: the xylem, which is closer to the center of the stem, and the phloem, located around the xylem, closer to the outside of the stem. how do these two structures work together in a living plant?

Identify the structure in organisms that do not have kidneys that is adapted to regulate water balance