Fill in the blanks apostrophe on phone not accepted as correct

Hi there, I created a fill in the blank exercise that works well on my laptop (mac) but on an Iphone, every word with an apostrophe is regarded as wrong when it is correct. However, it works normally on a Samsung smartphone.

Here's the link to the page where you can see the exercise (bottom of page).

http://yolainebodin.com/the-language-nook/english/question-tags-why-and-how-to-use-them

I have Wordpress 5.1 (but use classic version via plugin) and H5P Version 1.13.1

Thanks for your help