Jean is planning to take a foreign-language class. To research how satisfied other students are with their foreign language classes, she decides to take a sample of 50 such students. The university offers classes in five languages: Spanish, German, Russian, French, and Japanese. She will select a random sample of 10 students from each language. What best describes the sampling technique Jean is using?
a) a simple random sample
b) a stratified random sample
c) a voluntary response sample