Could some one help me out for question 7-10 please

PART I. Indicate whether each of the following statements is true (T) or false (F). If false, explain why. [20 points) 1 ] 1. A cross-sectional data set consists of observations on a variable or several variables over time. 1 12. An economic model consists of mathematical equations that describe various relationships between economic variables. I 13. The key assumption for the general multiple regression model is that all factors in the unobserved error term are correlated with the explanatory variables. 14. The coefficient of determination (R) decreases when an independent variable is added to a multiple regression model. I 15. H: & #0, where di is a regression coefficient associated with an explanatory variable, represents a one-sided alternative hypothesis. 16. If the absolute value of the t statistic is greater than the critical value, the null hypothesis, Ho is rejected in favor of the alternative hypothesis, H. I 17. Standard errors are always positive. I 18. When the zero conditional mean assumption fails, the usual t-test and F-test are invalid, while the OLS estimators are unbiased. I 19. If a random sample is drawn at each time period, pooling the resulting random samples gives us a panel data set. 110. Econometric model can be utilized for program evaluation and policy analysis