Although the school would receive financial benefits if it had soft drink vending machines in the cafeteria, we should not allow them. Allowing soft drink machines there would not be in our students' interest. If our students start drinking more soft drinks, they will be less healthy.

The argument depends on which of the following?

(A) If the soft drink vending machines were placed in the cafeteria, students would consume more soft drinks as a result.

(B) The amount of soft drinks that most students at the school currently drink is not detrimental to their health.

(C) Students are apt to be healthier if they do not drink soft drinks at all than if they just drink small amounts occasionally.

(D) Students will not simply bring soft drinks from home if the soft drink vending machines are not placed in the cafeteria.

(E) The school's primary concern should be to promote good health among its students.

read the answer options carefully to see what exactly the argument is saying - 

Counter Argument:

Soft drink vending machines in cafeteria --> financial benefits.

Author's argument:

students drink MORE Soft drinks --> LESS Healthy --> NO Soft drink vending machines in cafeteria

We have been asked to find an assumption for the author's argument.

Option A - correct answer.

If the author has to make his argument, then installing vending machines should lead to higher consumption of soft drinks.

Option B - Incorrect.

Whether the amount is detrimental or not is not relevant. All we are concerned about is whether the installation of vending machines leads to higher consumption of soft drinks and consequently makes students less healthy.

Moreover, negating this answer option kind of strengthens the author's argument. Hence, incorrect.

Option C - Incorrect.

this option is not relevant as we know already from the argument that installing vending machines leads them to drink MORE. this means that the amount they consumed earlier was not 0. 

That is the argument is making the comparison between consumption of some amount to more amount.

this option compares 0 to a small amount. What is applicable here need not necessarily apply to the argument.

Option D - Incorrect.

Even if they bring soft drinks from home, this option does not necessarily imply that they will drink more soft drinks than before. This means that they will still be MORE healthy than if the vending machines were installed.

The argument still stands after negation. Hence, incorrect.

Option E - Incorrect.

Nowhere is it stated that it is the "primary" objective. All we know is that it is an important goal. Whether it is the most important goal or not is unclear.