句子中成分的省略

Asked to nominate their ideal body figure, one in four children chose ideal body figures thinner than their perceived actual body.这句话中开头的Asked to...中是省略了 asked to...如此吗？若是，但为何when也省略了呢？

Asked to nominate their ideal body figure

=When asked to nominate their ideal body figure

= When they were askedto nominate their ideal body figure

【说明】最后一种使用方法是时间状语从句，需要用连词；前两种表达法是分词短语作时间状语，分词前面可以用连词，也可以不需要连词。