Assets here are : Home owned worth $105000, car owned worth $26000 , Investment fund worth $4500 and savings worth $1500
Liabilities are : mortgage owed worth $100000, car loan worth 22000 and credit card balance worth $15000
A positive net worth comes when total assets minus total liabilities are positive i.e more than zero.
Current net worth as per given scenario is :

=
(This gives zero net worth)
Checking option 1 - Lowering mortgage by $1000 , we get 137000-136000 = $ 1000 (positive net worth)
Checking option 2 - Increasing investment fund by $500 , we get 137500-137000 = $500 (positive net worth)
Checking option 3 - c. Adding $100 to savings , we get 137100-137000 = $100 (positive net worth)
Hence, all the options are correct.
D is the correct answer.