What is the main difference between active and passive sonar

There are two kinds of sonar: One is passive sonar, and the other is active sonar. For passive sonar, we don't send sound waves but just receive them. By listening to these special sound waves, animals that communicate with these particular sound waves can be detected. By listening to the sound waves from engines of submarines or ships, we can locate them.

Also, other things that vibrates can be detected by passive sonar. Many threats on the sea are usually detected by passive sonar this way. Since passive sonar does not transmit any thing to the environment, it does no harm to other animals. Active sonar is a little different.

Besides having a receiver, active sonar also transmits sound waves. Active sonar works by transmiting particular sound pulse and measuring the length of time for the sound to be reflected back, then devide the time by 2 to get the time it takes for the sound pulse to reach the object

i do not know and i have a 100 in this class

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."