The correct answer is 'the supplier is able to work at the same technical level as the buyer'. It's aboutbeing able to integrate the businesses together in terms of IT systems and such like.

gross profit = total revenue - cost of sales.
Learn all you can about financial ratios and financial statements for the exam- it's a very common topic

The correct answer is 'no - added value may change from one company to another'.
Added value is very subjective. What one person thinks is excellent added value, another may not rate highly.
For example one buyer may consider a supplier having good brand reputation as added value, but another might not care.
The other no answer is incorrect because added value can be tangible or intangible. Tangible means you can touch and see it and intangible means you can't.

The correct answers are 'it is easy to drive down costs' (as you can pit the suppliers against each other) and
'low risk of failure to supply' (if one supplier can't provide what you need, the other supplier might be able to).
Economies of scale and supplier loyalty are advantages of single-sourcing.
There is a risk of failure to supply is a risk associated with single sourcing.
There's a useful table of advantages and disadvantages of single / multi sourcing on p.22. Types of sourcing is a key topic for the exam.

This is a facilitation payment. It's when a sum of money is given for 'helping to facilitate' a contract. E.g. a procurement manager may accept a facilitation payment from a supplier for selecting him to be a new supplier for a big contract.
In the UK this is definitely considered a bribe. It's also against the CIPS Code of Conflict