Write this exercise either ___ ink or ___ pencil. Fill in the blanks with suitable prepositions:
(a)with / no preposition
(b)in / in
(c)by / by
(d)of / of

Hint: The meaning of the sentence is important because it will be easier to understand what is required. Understand the meaning and choose the preposition that
makes the most sense. Also, make sure that the sentence remains grammatically correct.

Complete answer:
Prepositions are words that are used to show positions, locations, direction, and time. They are usually placed in front of nouns and gerunds. Example - In the sentence ‘There is a book on the table’, the word ‘on’ describes the location of the book. So, it is a preposition. There are many verb + preposition combinations in the English language, which are easy to learn, like ‘get up’. Prepositions indicate the different relationships between other words in a sentence. They can be very important parts of a sentence, as they can give you important insight into the meaning of the sentence.
For example, in the sentence ‘We had a picnic at the park’, we understand where the picnic took place. It conveys that the picnic did not take place at any other location. This is an example of a preposition of location. There are many more types of
prepositions.
Understand the meaning of each preposition in the options:
The word ‘with’ is used for ‘accompanied by (another person or thing)’.
The word ‘in’ is used for ‘indicating the language or medium used’.
The word ‘by’ is used for ‘identifying the agent acting’.
The word ‘of’ is used for ‘expressing the relationship between a direction and a point of
reference’.

Now, we know what we are looking for. Let’s look at the given options:
(a)with / no preposition - These answers do not fit into the given sentence, as they don’t clarify the meaning. This is not the required answer. So, this is an incorrect option.
(b)in/in - These answers also fit into the given sentence, as they clarify the meaning. This is the required answer. So, this is the correct option.
(c)by/by - These answers also do not fit into the given sentence, as they don’t clarify the meaning. This is not the required answer. So, this is an incorrect option.
(d)of/of - These answers also do not fit into the given sentence, as they don’t clarify the meaning. This is not the required answer. So, this is an incorrect option.

Note: Six preposition rules : (i)A preposition must have an object, (ii) pre-position means place before, (iii) A pronoun following a preposition should be in object form, (iv)Prepositions have no particular form, (v) to preposition and to-infinitive are not the same, (vi) A preposition is followed by a "noun". It is NEVER followed by a verb.