<prompt> Translate the following text to EnglishVipimo vya kiwango cha chini cha uzalishaji vinavyoweza kuhifadhiwa kwa matumizi ya baadaye, vinaweza kubadilishana na vitu vingine katika mfumo, kuuza kwa vyanzo vingine au kuhifadhiwa kwa matumizi ya baadaye.  <response>: Units that reduce their emissions below the number of allowances they hold may trade allowances with other units in the system, sell them to other sources or save them for future use. 