Filtering Rows with duplicate column values

I was cleaning a dataset for class. I noticed there were some negative values. Some rows with this condition also have the same id name in two columns 2 and 3.

I'm stumped. I'm trying to draft out a code, but unsure where should I start. I would love to get advice. I couldn't find anything similar.

Below is a sample table similar to the table I have.

df <- data.frame(A=c(1,2,4,7,8), B=c(2,2,4,9,9), C=c(0,1,5,3,4))

Do I use the ifelse () nested within a filter()? Basically, I want to filter a data table without rows 2 and 3. I'm reading up on pipes currently. But what I'm learning so far doesn't seem to be a solution.