The proof, with a missing reason, proves that the measure of angle ECB is 54°. Which theorem can be used to fill in the missing reason?

Concurrency of Medians Theorem

Isosceles Triangle Theorem

Midsegment of a Triangle Theorem

Triangle Inequality Theorem

Identify all the cases where non-probability sampling is used when attempting to study the characteristics of a large city. studies on every subject in the population divide a population in groups and obtain a sample studies with a limited amount of time demonstrate existing traits in a population studies with the nth person selected