下列图形中，是中心对称图形的是[ ]

A．菱形

B．等腰梯形

C．等边三角形

D．等腰直角三角形

下列事件过程的功能是：建立一个名为Data1的随机文件，存放角度值及这些角度的正弦函数值和余弦函数值，角度为1，2，3，…，90。请在空白处填入适当的内容，将程序补充完整( )。
Private Type Ang
K As Integer
Sinx As Single
Cosx As Single
End Type
Dim Ksc As Ang
Private Sub Form_Click()
Dim Y As Single
Dim i As Integer
Dim Ksc As Ang
Open____________
Y=3.14159/180
For i=1 To 90
Ksc.K=i
Ksc.Sinx=sin(i*Y)
Ksc.Cosx=Cos(i*Y)
____________
Next i
Close #2
End Sub

A．"..\Data1.txt"For Random As #1 Len=10 Put#1, i, Ksc

B．"..\Data1.txt"For Random As #1 Len=10 Put#1, Y, Ksc

C．"..\Data1.txt"For Random As #1Put#1, i, Ksc

D．"..\Data1.txt"For Random As #1Put#1, Y, Ksc