ANSWER:

It is not mandatory to remain silent or to answer the athan. It is highly recommended to answer the athan and then recite the prescribed dua afterwards to be eligible for Prophet salla Allahu alaihi wa sallam’s intercession on the day of judgement, however this is not mandatory. 

Answer only one athan of the masjid that is nearer to you. 

In my locality we have many masjids and when there is time for adhan,every masjid uses their own loudspeakers for adhan call and each masjid give adhan at different times usually, my question is have i to answer each and every adhan or one adhan is enough, and can i continue my work after one adhan is over or i have to wait for each and every adhan to get over and till then remain silent.