In theory, risk investment cycle is determined by marginal added-value and marginal cost of projects.
理论上，风险投资周期由项目边际增加值和项目边际成本共同确定。
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In the middle-late stages of production, as the deepening of the oil field development, the marginal operation output decrease, the cost increases, and the investment increase, too.
Results The marginal seating of the casting without ring investment had significant difference compared with the castings with ring investment ( P< 0.05).