Which of the following statements is/are correct? 
1) In June 2016, the LIGO group of scientists announced the detection of a second set of gravitational waves. 
2) Gravitational waves were generated due to merger of two black holes at about 1.4 billion light-years distant. 
3) Gravitational waves were inserted due to collision of two white dwarf stars at about 1.4 billion light-years distant. 
Select the correct answer using the code given below.