Fill in the blank with the most appropriate word.

We cannot delay the project ______ it is urgent.

because

The correct word to fill in the blank is because.

• As if means in a manner or way that seems to be similar to something else. It is not the most appropriate word to use in this context, as it does not make sense to say that we cannot delay the project as if it is urgent.
• Than is used to compare two things. It is not the most appropriate word to use in this context, as we are not comparing the project to anything.
• Although means even though. It is not the most appropriate word to use in this context, as it does not make sense to say that we cannot delay the project although it is urgent.
• Because means on account of or for the reason that. It is the most appropriate word to use in this context, as it explains why we cannot delay the project.