at least seven occasions
... that tornadoes have passed through Washington, D.C., on at least seven occasions, and have damaged such landmarks as the United States Botanic Garden, the Smithsonian Institution, and the National Arboretum?
... that <a href="./Tornado" id="mwBn8" rel="mw:WikiLink" title="Tornado">tornadoes</a> have passed through <a href="./Washington,_D.C." id="mwBoA" rel="mw:WikiLink" title="Washington, D.C.">Washington, D.C.</a>, on <b id="mwBoE"><a class="mw-redirect" href="./List_of_District_of_Columbia_tornadoes" id="mwBoI" rel="mw:WikiLink" title="List of District of Columbia tornadoes">at least seven occasions</a></b>, and have damaged such landmarks as the <a href="./United_States_Botanic_Garden" id="mwBoM" rel="mw:WikiLink" title="United States Botanic Garden">United States Botanic Garden</a>, the <a href="./Smithsonian_Institution" id="mwBoQ" rel="mw:WikiLink" title="Smithsonian Institution">Smithsonian Institution</a>, and the <a href="./United_States_National_Arboretum" id="mwBoU" rel="mw:WikiLink" title="United States National Arboretum">National Arboretum</a>?