______ operate by distributing a workload evenly over multiple back end nodes. Typically the cluster will be configured with multiple redundant load-balancing front ends.

单项选择题（13）是（）

A.format
B.text
C.wave
D.center

单项选择题Maintenance activities include ______. ①making enhancements to software products ②developing a new software product ③correcting problems ④adapting products to new environments