铁树开花

Explanation: Tieshu: also known as cycads, evergreen trees, rarely flowering. Metaphor to very rare or extremely difficult to achieve. 　　Usage: The main predicate; as subject, object; describe things made hard 　　Source: To _set_ out the "Iron's Daughter": "Dayton Open parrot cage, twisting with the duck. Tieshukaihua also be taught that knot." 　　Examples: Japanese army crossing the Jinsha, cycads to flowering. (Chen Yi "Gannan guerrilla word") Thesaurus:  not likely to happen in a century, once in a blue moon, walk with difficulty, fish for a needle in the ocean; look for a needle in a haystack, Impossible and, Sea Fishing, Makes all things easy, bark [bay] at the moon [bay the moon], the sound of footsteps in a deserted valley-a news or a statement which one does not hear often,or a thing that was seldom to found, Rarities, once in thousand years, Hard-won, defy Beyond the bounds of, strength of nine bulls and two tigers,mighty force, doomed petition like asking a tiger for its hide, Leather and Fox plan Antonym Group:  Have no choice but Shengji, Just to stoop and gather Are all, as thick as June blackerries, ubiquitous, overrun, cataclysm crosscurrent, Attracting attention Are all, common and numerous, Even flat-bed truck