3 sentences

1. 这个计划能否成功还不得而知。

   zhè gè jì​huà néng​fǒu chéng​gōng hái bù​dé'ér​zhī.

   It is yet to be seen whether this plan will succeed or not.

   Source: Tatoeba

2. 他的真实动机，我们至今仍不得而知。

   tā de zhēn​shí dòng​jī, wǒ​men zhì​jīn réng bù​dé'ér​zhī.

   His true motives remain unknown to us to this day.

   Source: Dong Chinese Dictionary

3. 这种罕见的药材产于焉地，目前还不得而知。

   zhè zhǒng hǎn​jiàn de yào​cái chǎn yú yān dì, mù​qián hái bù​dé'ér​zhī.

   The origin of this rare medicinal herb is currently unknown.

   Source: Dong Chinese Dictionary