Some gardening books published by Garden Path Press recommend tilling the soil and adding compost before starting a new garden on a site, but they do not explain the difference between hot and cold composting. Since any gardening book that recommends adding compost is flawed if it does not explain at least the basics of composting, some books published by Garden Path are flawed.

The argument requires the assumption that

Astronomers have found new evidence that the number of galaxies in the universe is not 10 billion, as previously believed, but 50 billion. This discovery will have an important effect on theories about how galaxies are formed. But even though astronomers now believe 40 billion more galaxies exist, many astronomers’ estimates of the universe’s total mass remain virtually unchanged.

Which one of the following, if true, does most to explain why the estimates remain virtually unchanged?

Newspaper subscriber: Arnot’s editorial argues that by making certain fundamental changes in government we would virtually eliminate our most vexing social ills. But clearly this conclusion is false. After all, the argument Arnot makes for this claim depends on the dubious assumption that government can be trusted to act in the interest of the public.

Which one of the following most accurately expresses a flaw in the argument’s reasoning?

Columnist: Shortsighted motorists learn the hard wayabout the wisdom of preventive auto maintenance; such maintenance almost always pays off in the long run. Our usually shortsighted city council should be praised for using similar wisdom when they hired a long-term economic developmentadviser. In hiring this adviser, the council made an investment that is likely to have a big payoff in several years. Other cities in this region thathave devoted resources to economic development planning have earned large returns on such an investment.

Which one of the following, if true, most weakens the columnist’s argument?

Editorial: Cell-phone usage on buses and trains is annoying to other passengers. This suggests that recent proposals to allow use of cell phones on airplanes are ill-advised. Cell-phone use would be far more upsetting on airplanes than it is on buses and trains. Airline passengers are usually packed in tightly. And if airline passengers are offended by the cell-phone excesses of their seatmates, they often cannot move to another seat.

Which one of the following most accurately describes the role played in the editorial’s argument by the statement that cell-phone use would be far more upsetting on airplanes than it is on buses and trains?