A.an advice

数列1，0，1，0，…的一个通项公式是（　　）A.an=1+(-1)n2(n∈N+)

A clean bill is ______. A: a spotless bill B: A.a bill that is not accompanied by shipping documents C: A.an unused bill D: an invalid bill

Because the circulating water is in a closed loop,_______is installed to cater for expansion and contraction of the water at different conditions of operation. A.an expansion joint B.a drain tank C.a head tank D.a contraction tank

Which of the following is an instance of misuse of confidential information？（) A: A.An agent gives the seller the principal's name and phone number in a fully disclosed transaction B: B.A principal gives the contact details of an agent to a third-party without the agent's knowledge C: C.An agent withholds critical information from the principal about the agency D: D.An agent divulges private details of his past employer to his principal