fix typo

chapter_computer-vision/anchor.md

@@ -234,7 +234,7 @@ In practice, we can remove prediction bounding boxes with lower confidence level
 ## Exercises
 
 1. Change the `sizes` and `ratios` values in the `multibox_prior` function and observe the changes to the generated anchor boxes.
-1. Construct two bounding boxes with and IoU of 0.5, and observe their coincidence.
+1. Construct two bounding boxes with an IoU of 0.5, and observe their coincidence.
 1. Verify the output of offset `labels[0]` by marking the anchor box offsets as defined in this section (the constant is the default value).
 1. Modify the variable `anchors` in the "Labeling Training Set Anchor Boxes" and "Output Bounding Boxes for Prediction" sections. How do the results change?