It is mandatory that consumables should have … dates.

Step 1: Analyze the question The sentence says it is mandatory for consumables (food, drinks, drugs, and other goods we eat or use up) to have a particular kind of date. We need the word that correctly describes a date printed on such products.

Step 2: Explain the concept This tests your knowledge of compound words and common expressions. Before choosing, look at what each option means:

• Sell-by date: the date printed on a product showing the last day it should be sold or displayed in a shop. This is a standard phrase on packaged goods.
• Sell-out: a sale in which all the goods or tickets are sold (e.g. "The match was a sell-out"). It is not a date.
• Sell-off: the sale of goods at a low price, or the disposal of assets (e.g. a sell-off of government companies).
• Sell-on: reselling something you have bought to someone else. It is not tied to dates.

Step 3: Solve step by step

1. The blank is followed by "dates", so we need a word that forms a recognised phrase with "dates".
2. "Sell-out dates", "sell-off dates" and "sell-on dates" are not standard expressions.
3. "Sell-by date" is a standard expression, and it fits consumables because it protects buyers from expired products.
4. The sentence, "It is mandatory that consumables should have sell-by dates," is therefore correct and natural.

Step 4: Answer The correct option is A. sell-by.

Tip: Think of the labels on products in a supermarket: "Best before", "Expiry date", "Sell-by date". When a question talks about consumables and dates, think of these phrases. Also remember that "-by" shows a deadline (as in "sell by this date"), which makes it the right fit here.