-www.sciencebuzz.org
-pixabay.com
-https://www.google.com/search?q=the+history+of+sonar&oq=the+history+of+sonar&aqs=chrome..69i57j0l2.3977j1j7&sourceid=chrome&ie=UTF-8
-https://www.google.com/search?q=what+is+sonar&safe=strict&espv=2&biw=1366&bih=667&source=lnms&sa=X&ved=0ahUKEwjuwdjAmKDMAhVHkIMKHUiEB6EQ_AUIBSgA&dpr=1
-https://www.google.com/search?q=whales&safe=strict&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiuje_cmKDMAhVit4MKHbeuAkwQ_AUIBygB&biw=1366&bih=667#safe=strict&tbm=isch&q=dolphins+and+whales&imgrc=HL8Al-H-T1KzhM%3A
-https://www.google.com/search?q=fishing+boat&safe=strict&source=lnms&tbm=isch&sa=X&ved=0ahUKEwj42dKAmaDMAhWFlYMKHZGcDHsQ_AUIBygB&biw=1366&bih=667#imgrc=h5xg3w11lJ5
-www.gorillawire.com