Problem: Add spaces: Sevenperstem,fiveareadultsbynow.

Spaces added: Seven per stem, five are adults by now.
This text is missing some spaces, please add them: EnterthenewSIMcardPINandtapOK.
Enter the new SIM card PIN and tap OK .
input question: Fix spacing: Thisplotusesthe195483baseperiod.

output answer: This plot uses the 195483 base period.
Problem: Saturday10February,201861819676requestssinceTuesday16December,2003
What's a sentence that uses these characters?
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Saturday 10 February, 2018 61819676 requests since Tuesday 16 December, 2003
Add spaces: LaDioptriqueisaworkonopticsand,althoughDescartesdoesnotcitepreviousscientistsfortheideasheputsforward,infactthereislittlenew.Howeverhisapproachthroughexperimentwasanimportantcontribution.

Answer: La Dioptrique is a work on optics and, although Descartes does not cite previous scientists for the ideas he puts forward, in fact there is little new. However his approach through experiment was an important contribution.
This text is missing some spaces, please add them: Onemillionmillionmillion-FreeEnglishonlinedictionarybasedonWordNet3.0
One million million million - Free English online dictionary based on WordNet 3.0