Originally Posted by omerkhan

german silver is alloy of copper, nickel and zinc so the answer is none of these

convection is heat transfer in liquids, so the answer to the first one should be radiation

Sonar uses ultrasound

rainfall is measured by none of these, bcuz its measured by rain guage

twinkling of stars is due to interference, just checked it on wikipedia

Twinkling of stars are a phenomenon of REFRACTION
check it on www.enchantedlearning.com/subjects/.../stars/twinkle.shtml

escape velocity is 7 miles/sec

these are the ones that I am very sure about.