Answer:
Option c
Step-by-step explanation:
In Statistics, both t and z tests are used for testing of hypothesis.
Whenever we have sample sizes >30 and when we know population std deviation sigma, we use Z test.
i.e. if sigma is known, we check whether sample size >30 then we use z test
Otherwise if population std deviation is not known, we use t test.
Even if population std deviation is known, if n <30 we use t test. Both use the same formula for std error.
Hence the correct option is option c.
