Fill in the blank with a suitable verb.
Two bags of rice ______ only 7 pounds.
(a)costs
(b)cost
(c)costing
(d)have costing

Hint: The given sentence is in the assertive form, meaning it is a simple statement being made. This means that the verb should be in the simple present tense.

Complete answer:The simple present (also called present simple or present indefinite) is a verb tense which is used to show repetition, habit or generalisation. Less commonly, the simple present can be used to talk about scheduled actions in the near future and, in some cases, actions happening now.

The simple present can also indicate the speaker believes that a fact was true before, is true now, and will be true in the future. It is not important if the speaker is correct about the fact. It is also used to make generalisations about people or things.
The simple present is just the base form of the verb. The suffix added depends on the subject’s plurality.
Now, we know what we are looking for, let’s look at the available options:
(a)costs - The word ‘costs’ is in the simple present tense. However, it is used only for singular subjects. This does not fit into the given sentence. This is not the required answer. So, this is an incorrect option.
(b)cost - The word ‘cost’ is in the simple present tense. This form is used with a plural subject. This fits perfectly into the given sentence. This is the required answer. So, this is the correct option.
(c)costing - The word ‘costing’ is in the present continuous tense. This does not fit into the given sentence. This is not the required answer. So, this is an incorrect option.
(d)have costing - This phrase is grammatically incorrect. This does not fit into the given sentence. This is not the required answer. So, this is an incorrect option.

Note: Try to look for certain pointer words. They will help you understand which option you are looking for. Then, go through the given options, and choose the most appropriate option accordingly.