This kind of letter explains that changes must be made before an application can be approved, with no guarantee regarding the its ultimate approvability.

在这封信中，FDA解释说在投入应用之前，配方需要改进，但不保证最终的获批。

youdao

Provide letter of credit (L/C) service and guarantee;

提供信用证服务及担保；

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For example, no one reading this letter can guarantee that they will be alive the next day.

ECONOMIST: When I'm 64

In recent days, students at Duke University, Apple CEO Tim Cook's alma mater, published an open letter calling on Cook and Apple to guarantee "conflict-free" products.

CNN: Apple, consumers must urge worker justice

Gennady Onishchenko, Russia's chief sanitary official, told Ekho Moskvy radio that he has sent a letter to the European Commission requesting a guarantee that meat products sold to Russia don't contain horse meat.

NPR: Russia Seeks EU Guarantees Over Horse Meat Scandal