Step 1: The task.
Pick the two correct statements about flowers.
Step 2: Statement A.
A says the thalamus margin grows up and fully encloses the ovary in cucumber. This describes an epigynous flower, and cucumber is a good example. So A is correct.
Step 3: Statement B.
B says the calyx is green and leaf like and protects the flower in the bud stage. That is the standard job of the calyx (the sepals). So B is correct.
Step 4: Statement C.
C says a Canna flower can be cut into two equal halves by any vertical plane. This is wrong, because Canna flowers are asymmetrical and cannot be divided equally in any plane. So C is incorrect.
Step 5: Statement D.
D says in Cassia the sepal margins overlap in one particular direction. Cassia actually shows imbricate aestivation, which does not follow one fixed direction. So D is incorrect.
Step 6: Conclusion.
The correct statements are A and B. Therefore the correct answer is "A, B". \[ \\boxed{\\text{A, B}} \]