Strict Standard error message while adding questions

Hi When i click to add question , i get the following error. It doesn’t stop me to add questions but when i copy short code on my page same error message displayed again between question and multiple choices.

Please help

Strict Standards: Accessing static property Wpsqt_Question_Multiple::$_id as non static in /homepages/24/d411980498/htdocs/wp-content/plugins/wp-survey-and-quiz-tool/lib/Wpsqt/Question/Multiple.php on line 19

Strict Standards: Accessing static property Wpsqt_Question_Multiple::$_id as non static in /homepages/24/d411980498/htdocs/wp-content/plugins/wp-survey-and-quiz-tool/lib/Wpsqt/Question.php on line 93

Strict Standards: Accessing static property Wpsqt_Question_Single::$_id as non static in /homepages/24/d411980498/htdocs/wp-content/plugins/wp-survey-and-quiz-tool/lib/Wpsqt/Question/Multiple.php on line 19

Strict Standards: Accessing static property Wpsqt_Question_Single::$_id as non static in /homepages/24/d411980498/htdocs/wp-content/plugins/wp-survey-and-quiz-tool/lib/Wpsqt/Question.php on line 93

Strict Standards: Accessing static property Wpsqt_Question_Freetext::$_id as non static in /homepages/24/d411980498/htdocs/wp-content/plugins/wp-survey-and-quiz-tool/lib/Wpsqt/Question/Freetext.php on line 18

Strict Standards: Accessing static property Wpsqt_Question_Freetext::$_id as non static in /homepages/24/d411980498/htdocs/wp-content/plugins/wp-survey-and-quiz-tool/lib/Wpsqt/Question.php on line 93

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