Step-by-step explanation:
In the given context, both "discount" and "on sale" are appropriate terms to describe a situation where the price of the shirt is lower than its original price. You can use either term based on the specific context you are describing:
Discount: If you want to emphasize that the reduced price is due to a specific percentage or amount being deducted from the original price.
Example: "This shirt is cheaper than its original price. It's discounted by 20%."
On Sale: If you want to emphasize that the item is available for purchase at a reduced price without specifying the exact reduction.
Example: "This shirt is cheaper than its original price. It's on sale for $30."
Both answers are correct depending on the emphasis you want to convey in your statement.