求翻译：The challenges facing china today come from several sources.A rapidly growing economy is very forgiving: property rights may not have to be well-defined to elicit high levels of investment, if the payback period on investments is two or three years. but those high returns cannot be sustained, and as returns come down,investors will look more carefully at the long-run security of their investments.this will necessitate the development of a better institutional infrastructure.是什么意思？

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