Econometrics questions

I need help with question #15, #18, #19 and 25-28. also, 

1. to adjust a model for serial correlation, one would use: 

        a. the Goldfel-Quandt method 

       b. a dummy variable approach

       c. weighted least squares 

       d. the Cochrane-Orcutt procedure 

2. Multicollinearity may result in: 

       a. elevated t-values 

        b. incorrect sign associated with a parameter estimate 

        c. a and b 

       d none of above