Correct Answer: contact

Solution : The correct option is the first option.

Contact is when two things physically touch or come into contact with each other. In this context, it implies direct touching or interaction between nickel or brass and human skin, which can cause an allergic reaction.

The meanings of the other options are as follows:

• Surface means the outer or topmost layer of an object.
• Accordance means agreement or conformity with something else.
• Parallel means side by side and having the same distance between points along their lengths.

Therefore, the complete sentence would be: "Nickel or brass can cause an allergic reaction when in contact with human skin."