Hello everyone.

I'm editing a Stack question, and I've added a drop down input.

All the variables all here (in case the problem can be connected to them):

cx1: rand_with_step(14,21,1);

Vx: rand([200,250,300,350,400,450,500,550,600,650,750]);

cx2: rand_with_step(2,9,1);

vztah_V: (c2*Vv)/c1

ta1:  vztah_V;

unit: ((dm^3));

stack_unit_si_declare(true);

prem: (Vx/1000);

ta2: decimalplaces(subst([c2=cx2,Vv=prem,c1=cx1],vztah_V),2);

ta3: ([mol,true],[kg,false],[km,false]);

This last variable (ta3) is the problematic one.
The question to this variable in the question text part is: 3.) Choose the correct unit for amount of substance input:ans3 validation:ans3 feedback:prt3

I set input ans3 to Drop down list input type, and the model answer is ta3. In the response tree prt3: answer test is AlgEquiv, SAns: ans3 and the TAns: mol.

The preview says: The input has generated the following runtime error which prevents you from answering. Please contact your teacher. The model answer field for this input is malformed: [km,false]. The teacher did not indicate at least one correct answer.

Can anyone spot the problem? Thank you in advance.