TOEFL Reading: ETS-TOEFL阅读机经 - 631MA49JZBR27B7ZL$

According to paragraph 6, one of the types of electroreceptors of the elephantnose fish shuts down at times in order to A. avoid confusing its own signals with those of other fish B. prevent the receptor from becoming damaged C. distinguish between signals of short and long duration D. enable the fish to produce echoes of the discharges of other fish