Which of the following statement is correct?

Which of the following statement is correct?
a) E2 is a concerted reaction in which bonds break and new bonds form at the same time in a single step
b) Order of reactivity of alkyl halides towards E2 dehydrohalogenation is found to be 3o > 2o > 1o
c) In E2 elimination different stereoisomer (diastereomer) converts into different stereo product
d) All of the mentioned

Answer:
d) All of the mentioned