What are any possible bias in the following situations: a) Year 7 students are interviewed about changes to the school uniform
b) Motorists stopped in peak hour are interviewed about traffic problems
c) Real estate agents are interviewed about the state of the country's economy
d) Politicians are interviewed about the state of the country's economy
e) People are asked to phone in to register their vote on an issue
f) An opinion poll is conducted by posting a questionnaire to people
g) an advertisement claims that "Dog breeders recommend Puppy Meats Dog Food."