Five companies worked together to increase the project price. Usually the work can be finished at $2 million. The five companies submitted the bid for $1.4, $1.8, $1.9, $2.0 and $1.5 million to ensure the lowest one successfully won the bid. What is the scheme? Select one: a. Bid rigging with insider employee collusion b. Complementary bid c. Bid rotation X d. Bid suppression