Dung is kind and helpful, but he is also
题型：选择题
问题：
Dung is kind and helpful, but he is also a little careless _____________.
A．at time
B．at a time
C．at times
D．once a time
Dung is kind and helpful, but he is also a little careless _____________.
A．at time
B．at a time
C．at times
D．once a time