The features to define angiosperms and gymnosperms should be ones which the other lacks in an unambiguous manner. Angiosperm traits: flowers, fruits, endosperm. Gymnosperm: cones or similar non-fruit structures, 2n nutritive tissue in the seed.
Work Step by Step
To answer this, scan through the chapter for obvious defining features which one group or the other has. Make two lists, one for each group.