@article{ref1,
title="Sport activities of twins",
journal="Acta gerontologica (Milano)",
year="1955",
author="Grebe, H.",
volume="4",
number="3",
pages="275-296",
abstract="<p>[Abstract unavailable]</p><p>Language: de</p>",
language="de",
issn="0001-5741",
doi="",
url="http://dx.doi.org/"
}