单项选择题

Task 1 Directions: After reading the following passage, you will find 5 questions  or unfinished statements, numbered 36 to 40. For each question or statement there are 4 choices marked A),B),C)and D). You should make the correct choice and mark the corresponding letter on the Answer Sheet with a single line through the center.        
The contract of employment is the agreement made between the employer and the employee. This could be a written agreement or in an oral form.      
In addition, the contract will also include “custom and practice ”agreements. These are how things are usually done in the workplace, for example, if the employer always gives the employees a day’s holiday in August. Even though this is not mentioned in the written contract, this will from part of the contract as it is the usual practice.      
A trade union may have negotiated(谈判达成）an agreement with an employer about conditions at work. The negotiated agreement will often from part of a contract.     
Some contracts will be illegal if:     
*the employee gets all or part of their wages in cash;    
*tax and national insurance contributions(国民保险税）are not paid; and  
*the employee knows they are getting paid in this way to avoid paying national insurance and tax.

According to the passage, the trade union and employer may negotiate an agreement on （）.

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