请问41题是不是只能填shown,不能填showed？

Research
has 41 (show) that children who lack friends can suffer from emotional and
mental difficulties later in life. They have also found that children with friends have a 42
(great) sense of happiness, better self-esteem and f ewer problems as they grow up.

是的，41题应该填shown而不能填showed。因为使用了has，表示动作是在现在完成时发生的，而shown是过去分词，在现在完成时中作谓语动词的时候需要用到过去分词形式。而showed则是过去式，表示过去某个时间做出的动作，与现在完成时的语态不符。