Now is an excellent time to invest in the catering business. A survey

70% readers of Weddings magazine want a catered wedding.
Current number of caterers can serve only 55% of weddings.

Conclusion: Invest in catering business.

What is a weakness? What will say that investing in catering may not be a good idea.
The argument depends upon "demand (70%) is more than the supply (55%)".

But what if this sample size doesn't represent the population? i.e. people who buy and read Wedding magazine might be those who want a well planned wedding. That is why they bought the magazine to learn how to plan it well. Then they are more likely that the regular population to want a catered wedding.
Out of 100 weddings planned, say 10 people bought the magazine. These 10 are likely to be the ones who want to plan their wedding v well. If 7 of them want a catered wedding, can we say that total 70 out of 100 want a catered wedding? Most likely no.

Hence, option (D) is correct. Rest all options are irrelevant.