数式は得意ではありませんが、これで十分です
=IF(LEN(B1)>0,IF(B1="low","Yes",IF(B1="medium",IF(C1<>"please fill in",IF(C1<>"","Yes","No"),"No"),IF(B1="high",IF(B1<>"please fill in",IF(LEN(C1)>0,"Yes","No"),"No"),"No"))),"No")
VBA関数が必要な場合(ただし、各セルに数式を個別に入力する必要がある場合は、これをモジュールに貼り付けてから、列Aで使用します
Function CheckIt() As String
Dim r As Long
r = ActiveCell.Row
If Range("B" & r) = "low" Then
CheckIt = "Yes"
Else
If (Range("B" & r) = "medium" Or Range("B" & r) = "high") Then
If ((Range("C" & r) <> "please fill in") And (Not IsEmpty(Range("C" & r)))) Then
CheckIt = "Yes"
Else
CheckIt = "No"
End If
Else
CheckIt = "No"
End If
End If
End Function
例
