It would be D:
While I was at the gym—wondering what machine to use next—I ran into my neighbor.
It can be proven using objective evidence
If raining lunchtime, (I'll remain indoors. )
Or
If it's raining at lunchtime time, (I'll remain indoors.)
(when you know it may rain)
Or
If it rains lunchtime, (I'll remain indoors. )
(when you're not sure it's going to rain)
Hope this helps!
D. instructions for taking apart a clock to repair it
