'~' character not appearing in quiz questions

[sof202]

Questions 6,7 and 8 should have a ~ character in them:

Example:

cfrrRtutorials/inst/tutorials/Introduction to Regression with R/Introduction-to-Regression-with-R.Rmd

Line 731 in b83cec6

question("For the full model $y ~ age + education_years$, which of these are valid null models? Select all that apply",

However, when rendered, they do not:

This is because ~ is a reserved character in many LaTeX parsers. In the past I have used $\sim$ to get around this issue.