单选题：Which of the following statements is FALSE?
Which of the following statements is FALSE?
A.A directed acyclic gragh must be a tree.
B.There must be no topological order in a directed graph with a cycle.
C.Topological sorting method can be used to check if there is a cycle in a given directed graph.
D.Partial order is a precedence relation which is both transitive and irreflexive.
答案：A
A.A directed acyclic gragh must be a tree.
B.There must be no topological order in a directed graph with a cycle.
C.Topological sorting method can be used to check if there is a cycle in a given directed graph.
D.Partial order is a precedence relation which is both transitive and irreflexive.
答案：A
