C. The total column widths exceed 12 units, causing layout issues
D. The columns should use 'col-md-' instead of 'col-'
Solution
Step 1: Calculate total column units
col-3 + col-6 + col-4 = 3 + 6 + 4 = 13 units, which is more than 12.
Step 2: Understand Bootstrap grid limits
Bootstrap grid rows can only hold 12 units total; exceeding causes wrapping or broken layout.
Final Answer:
The total column widths exceed 12 units, causing layout issues -> Option C
Quick Check:
Sum of col-* > 12 breaks layout [OK]
Hint: Sum col-* classes must be 12 or less per row [OK]
Common Mistakes:
Ignoring total column width sum
Confusing container and row classes
Thinking 'col-' is invalid syntax
5. You want a Holy Grail layout with a header, footer, and three columns in the middle using Bootstrap. The left and right columns should be narrow on desktop but stack vertically on small screens. Which Bootstrap classes combination achieves this?