Problems with the join and separate structures, with the start or initial amount unknown, tend to be the hardest for young students to understand and accurately solve. Identify the reason for they are more challenging for young children to use .A) Children can model the physical action.
B) Children can act out the situation.
C) Children cannot use counters for the initial amount.
D) Children cannot grasp a quantity represents two things at once.

C) Children cannot use counters for the initial amount.

Step-by-step explanation:Problem solving allows students to use mathematical concepts, skills and the relationships among them to solve problem situations with different levels of difficulties. Problem solving framework allows students to solve mathematical situations by assisting them to handle or approach problem solving systemically.

There are basically four structures they are

(1) Join

(2) Separate

(3) Part-Part-Whole

(4) Compare.

JOIN AND SEPARATE STRUCTURES INCLUDE ACTIONS THAT INCREASE OR DECREASE A QUANTITY.

The part-part whole does not involve an action but it has a relationship between a particular whole and its two separate parts.

The compare structure also does not involve an action,but it compares two unconnected and distinct sets.