Let's look at each sentence to determine how the modal verb affects the meaning:
We could work together on the science project.
Here, the modal verb 'could' indicates possibility, not certainty. So, we will tick the box under 'Modal verb indicates possibility'.
Drew will help you to tidy your garden.
In this sentence, the modal verb 'will' indicates certainty. Therefore, we will tick the box under 'Modal verb indicates certainty'.
Li might have missed the bus because she is late.
The modal verb 'might' suggests possibility. As such, we tick the box under 'Modal verb indicates possibility'.
Now, let's write a sentence using a modal verb to indicate obligation:
You must submit your homework by the deadline.
In this sentence, the modal verb 'must' is used to indicate an obligation, meaning it is necessary or required to submit your homework by the deadline.
The analysis of the sentences shows that 'could' and 'might' indicate possibility, while 'will' indicates certainty. An example sentence demonstrating obligation is 'You must finish your project before the due date.' This conveys the necessity of completing the project on time.
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