Deltoid Composition Analysis: Isosceles and Right Triangle Properties

In order to answer the question asked first, we need to recall some properties of the deltoid. For this purpose, let's draw deltoid $ABCD$ where we connect every two non-adjacent vertices (meaning - draw the diagonals) and mark the intersection of the diagonals with the letter $E$:

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Let's recall two properties of the deltoid that will help us answer the question (markings from the previous drawing):

a. Definition of a deltoid - A deltoid is a convex quadrilateral with two pairs of adjacent equal sides:

$BA=BC\\ DA=DC$

b. The diagonals in a deltoid are perpendicular to each other:

$AC\perp BD\\ \updownarrow\\ \sphericalangle BEA= \sphericalangle AED= \sphericalangle DEC= \sphericalangle CEB=90\degree$

Now we can clearly answer the question that was asked, and the answer is that the deltoid can indeed be described as composed of two isosceles triangles since triangles: $\triangle ABC,\hspace{6pt}\triangle ADC$ are isosceles - (from property a' mentioned earlier):

Or can be described as composed of four right triangles, since triangles: $\triangle AEB,\hspace{6pt}\triangle CEB,\hspace{6pt}\triangle AED,\hspace{6pt}\triangle CED$ are right triangles (from property b' mentioned earlier):

Therefore, the correct answer is answer a'.