What is the reasoning behind this logic question?

Can anyone explain the answer to this question below? I know the answer is C, but I don’t understand why. Also, does anyone know of a logic workbook that would have similar questions with answers so I can practice?

#1 Sample Question:

Premises: If housing starts are up this year, lumber sales at Merrihew Lumber should increase and the company, on shaky grounds for the past several years, will not have to declare bankruptcy. If Merrihew does go out of business, United Building Supplies will have increased lumber sales and will phase out their masonry line. Conclusion: If housing starts are down this year, United Building Supplies will not phase out their masonry line.

a. necessarily true.
b. probably, but not necessarily, true.
c. indeterminable, cannot be determined.
d. probably, but not necessarily, false.
e. necessarily false.