求一段选词填空解释,It is thought that if the brain is busy focusing o

求一段选词填空解释,
It is thought that if the brain is busy focusing on many aspects of a task,it has to ____ its resources,and pays less attention to the clock.______,time passes without us really noticing it.
第一个空填spear还是focus,第二个空填however还是therefore,