reserves
... that Serbia has large but undeveloped reserves of oil shale?
... that <a href="./Serbia" id="mwB_k" rel="mw:WikiLink" title="Serbia">Serbia</a> has large but undeveloped <b id="mwB_o"><a href="./Oil_shale_in_Serbia" id="mwB_s" rel="mw:WikiLink" title="Oil shale in Serbia">reserves</a></b> of <a href="./Oil_shale" id="mwB_w" rel="mw:WikiLink" title="Oil shale">oil shale</a>?