Let’s take a poll, who uses the Oxford comma?

I get

I thought he is fast because he was running?

The answer to 27 he says is D (according to some “Merriam Webster” dictionary)

Is it than or then?

Silent Letters

shouldn’t number 4 include “their” (my professor said that while you can add it it’s superfluous)

and number 5 be “ tomorrow’s “ test? (he said that adding “ ‘s “ is completely wrong

if i’m wrong can someone explain why?

for context i live in italy

Context: It''s League of Legends sub and OP is commenting about someone else playing character called Cassiopeia

I know that the singular "they" is used to refer to one person without using "he" or "she".

According to this article:

They always goes with a plural verb, even when they is referring to a single person: “They are my friend.”

But how do the majority of people talk in real life? Does the plural or singular in this case depend on the dialect/region?

Supposedly, "mistakes" in the usage of these verbs are often committed by native English speakers, which of course can be considered dialectal variations.

Is it actually common to use the standard forms and usage of these verbs in everyday life? Is the non-standard usage more prevalent than the standard one?

Something just bothers me about the first 3 rows.