Three Sons-in-Law

An old woman had 3 daughters. One day she decided to test her three Sons-in-law.
One a fine day, she was walking along a lake shore with the first son-in-law. Purposefully, she fell down in the lake and started yelling for help.
The first son-in-law jumped into the water and dragged her out into the shore. The next day he found a brand new E Class Mercedes in his door steps with the wordings “Thank you! Your Mother-in-law who loves you very much!!”
Another day she went out with her second son-in-law. Purposefully, she fell down in the lake and started yelling for help.
The second son-in-law too jumped into the water and dragged her out into the shore. The next day he found a brand new E Class Mercedes in his door steps with the wordings “Thank you! Your Mother-in-law who loves you very much!!”
The third time she was walking with the third son-in-law and she repeated the same. But that guy got scared and ran away without offering any help to her. The poor old lady who wanted to test her sons-in-law drowned and died.
The next day the third son-in-law was surprised to see a new brand new Rolls-Royce waiting at his doorsteps with the following wordings, “Thank you very much! Your Father-in-law!”