Explanation:

Introduction:
This question is asking which option correctly completes the sentence "We __________ reach by 7 PM before the ceremony starts." In other words, which option indicates that it is necessary for us to arrive before 7 PM.

Analysis of Options:
Let's analyze each option to determine whether it fits the context of the sentence:

a) must: This option indicates a necessity or obligation. If we use "must" in this sentence, it means that it is necessary for us to reach our destination before 7 PM. This option is the correct answer because it correctly conveys the idea that reaching before 7 PM is a requirement.

b) might: This option indicates a possibility or uncertainty. If we use "might" in this sentence, it means that it is possible for us to reach before 7 PM, but it is not certain. This option does not accurately convey the idea that reaching before 7 PM is necessary.

c) could: This option indicates a possibility or ability. If we use "could" in this sentence, it means that we have the ability to reach before 7 PM, but it is not necessary. This option does not accurately convey the idea that reaching before 7 PM is required.

d) dare: This option is not appropriate in this context. "Dare" is typically used to express a challenge or invitation to do something risky or bold. It does not fit the meaning or requirement of the sentence.

Conclusion:
Based on the analysis of the options, option 'A' (must) is the correct answer. It accurately conveys the idea that it is necessary for us to reach our destination before 7 PM.