Must be false. One starting fact is that investment is not decreasing. And since investment is not decreasing, that implies unemployment is not rising, which in turn implies the economy is not weak. So the economy is not weak, and investment is not decreasing.

Could be true. We don’t know whether unemployment rising implies that prices remain constant. Both are things that are implied by a weak economy. But there may or may not be a relationship between the two directly.

Must be true. If economy is weak, that requires unemployment rising, which requires investment decreasing.

Could be true. Although we can infer that the economy is not weak, it’s possible for prices to be constant. A weak economy implies that prices are constant, but it’s possible that a non-weak economy can also exist with constant prices.

Must be true. We know that investment is not decreasing, which implies unemployment is not rising, which in turn implies the economy is not weak. So, the “economy is not weak” part of (E) must be true. When one part of an “or” statement is true, the “or” statement itself is true.