In which one of the following examples could X be modelled by a Binomial random variable?
(a) A group of six friends go to Mr Waffle, X is the number of the group that order a hot chocolate
(b) 20 water samples are taken from a river at different distances downstream from a factory, X is the number of samples that test positive for the presence of a pollutant produced by the factory
(c) Calls arrive at a call centre as a random process, X is the number of calls arriving between 9 am and 5 pm
(d) Ten medical devices are selected as a simple random sample from a production line, X is the number of defective devices in the sample.