You can usually tell the difference between a caldera and crater by studying

-a feature's size and formation
-if a feature is filled with water or not
-a feature's size and shape
-if a feature is a cinder cone volcano

You can usually tell the difference between a caldera and crater by studying a feature's size and formation. In terms of size, a caldera is often relatively larger than ordinary craters. A caldera is so big that it causes explosive eruptions. In terms of formation, a caldera is a large depression caused when a magma chamber is emptied. A crater is a bowl-like formation at the top of volcanoes where lava comes out.

Well, a and b together would be negative. b alone would also be negative.

The time of day would be around 3: 00