Please use the preset() function (above the question/s on the same page) to pre-select options.
Here is an example for 3 single choice question AB01, AB02 and AB03.
preset('AB01', 3);
preset('AB02', 2);
preset('AB03', 1);
Please note that the variable names may look different (e.g. 'SK01_01' oder 'SF01x1') depending on the question type.