22: B
The prompt says that "the resulting lack of substance leads to books that are short-lived." If lack of substance leads to lack of longevity, then we can conclude that substance is necessary for longevity.
23: A
The author is assuming the because low left lobe levels and depression are correlated, the former causes the latter. We can weaken this causal relationship by establishing that 1) Depression causes a loss of left lobe activity (b, e), 2) Some other root cause is responsible for both effects (d), or 3) the findings are simply coincidence and the relationship isn't reliable (c). A, meanwhile, indicates that depresion can be fought by raising left-lobe levels, strengthening the conclusion that lobe levels control disposition.
24: A
The authors conclusion is that what is important to a painting is what it presents to experience rather than what it symbolizes (we know this by the keyword therefore). His evidence is that extrinsic properties are unimportant, and intrinsic properties are key.
Because he's shifting from irrelevant extrinsic properties in his evidence to irrelevant symbolism in his conclusion, it MUST be true the symbolism is extrinsic; if any symbolism is intrinsic, then his logic is flawed.
