Use ‘it can’ or ‘it can’t’.
If something is unbreakable, it _______.
a. can be broken
b. can’t be broken
c. can be breakable
d. can be able to break

Hint: The options differ in meaning, as some are negative and some are not. The option that clarifies the meaning of the sentence will be the correct answer. Choose an option accordingly.

Complete answer: We already know the meaning of ‘unbreakable’. This word has a negative meaning, as it is a negative concept. It is the absence of breakage. So, we need a negative modal auxiliary.

The meaning of ‘can’ itself is ‘to be able to’. So, it would be redundant to use that phrase again. The participle of ‘break’ is necessary. Now we know what we are looking for. Let’s look at the given options:
a. can be broken - This option is a positive phrase. This phrase makes use of the correct participle and construction, but it is not the required answer as it is not negative. So, this is an incorrect option.
b. can’t be broken - This option is a negative phrase. This phrase makes use of the correct participle and construction and it fits perfectly into the given sentence. This is the required answer. So, this is the correct option.
c. can be breakable - This option is a positive phrase and it is constructed incorrectly. It does not use the correct participle. This does not fit into the given sentence. It is grammatically incorrect. This is not the required answer. So, this is an incorrect option.
d. can be able to break - This option is a positive phrase and it is constructed incorrectly. It does not use the correct participle. This does not fit into the given sentence. It is grammatically incorrect. This is not the required answer. So, this is an incorrect option.

Thus, Option B is a right answer.

Note: The word ‘unbreakable’ refers to ‘not liable to break'. This word is very clearly conveying one meaning. The options also have different phrasing and different participles. Make sure that the sentence remains grammatically correct.