Final answer:
The correct answer is option d. improves/have/had.
Step-by-step explanation:
The correct answer to complete the sentences is d. improves/have/had.
This is the correct option because the verb tense remains consistent throughout the sentence. 'Improves' is in present tense to show the current state of the economy. 'Have' is used to indicate a general opinion. 'Had' is used to show that the trouble has been ongoing for some time. This option provides a grammatically correct and coherent sentence.
For example, the completed sentence would read: 'The economy improves these days, but I think we have some trouble for some time in the near future.'
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