设a是最小的自然数，b是最大的负整数，c是绝对值最小的有理数，a，b，c三个数的和为 [ ]
A．﹣1
B．0
C．1
D．不存在
答案：A
Walmart, which is one of the largest American supermarket chains, _______ some of its store open 24 hours on Mondays through Saturdays.
A．keep
B．keeps
C．have kept
D．had kept
连锁经营的内涵是什么，如何看待连锁经营从低级化向高级化发展？
