When a student completes it and then submits the test/quiz, this problem is marked incorrect and shown as if they never attempted it even if they chose the correct answer.

See the problem below for an example.

Can anyone help me figure out what is going wrong on this problem?

Thanks!

Problem code:

DOCUMENT();

loadMacros(

"MathObjects.pl",

"PGstandard.pl",

"parserMultiAnswer.pl",

"PGcourse.pl",

"PGchoicemacros.pl",

);

TEXT(beginproblem());

$showPartialCorrectAnswers = 1;

######################

# SETUP #

$mc = new_multiple_choice();

$mc -> qa (

"If \(\nabla{f(x,y)}\) is not the zero vector and \(\lambda\) is a constant scalar, what does this equation tell us about the geometric relationship between these two gradient vectors?",

"They are parallel");

$mc -> extra ( "They are the same vector",

"They are orthogonal",

"They share a common initial point");

$mc -> makeLast ("None of the above");

# END SETUP #

######################

######################

# MAIN TEXT #

Context()->texStrings;

BEGIN_TEXT

$BR

$BBOLD Intro $EBOLD

$BR

Use the following link to open the Multivariable Calculus Exploration applet in a new window. The Lagrange Multiplier Exploration should open up automatically within this applet. Some instructions will appear in a small dialog window to the right of the screen. Use the applet to answer the questions below. You will need to switch back and forth between the applet and this browser window. As you go along, enter your answers to these questions below. You may find it helpful to use the associated application icons at the bottom of the screen.

$PAR

\(\nabla{f(x,y)}\) = \(\lambda\nabla{g(x,y)}\)

$PAR

\{$mc -> print_q() \}

$BR

\{$mc -> print_a() \}

END_TEXT

Context()->normalStrings;

# MAIN TEXT END #

######################

#############################

# ANSWER EVALUATION #

$showPartialCorrectAnswers = 0;

ANS( radio_cmp( $mc->correct_ans() ) );

# ANSWER EVALUATION END #

#############################

ENDDOCUMENT();