Understanding suffixes is an important part of English grammar, as they are word endings that can change a word's meaning or its grammatical function. The question asks us to identify a single suffix that can be added to all the given words: Use, truth, and care, to form new, valid words.

Suffix Definition and Purpose

A suffix is a letter or group of letters added to the end of a word to form a new word. This new word often belongs to a different grammatical category (e.g., noun to adjective) or has a modified meaning. For example, adding '-ful' to a noun like 'care' creates the adjective 'careful', meaning 'full of care'.

Word Matching with Suffixes

To find the correct suffix, we will systematically test each option provided with all the base words: Use, truth, and care.

Option Analysis: The Suffix "-ful"

Let's apply the suffix "-ful" to each of the given words:

• Use + -ful = Useful (meaning: able to be used, serving a purpose)
• Truth + -ful = Truthful (meaning: telling or expressing the truth)
• Care + -ful = Careful (meaning: exercising caution, taking care)

As we can see, adding "-ful" successfully creates valid and meaningful English words from all three base words: useful, truthful, and careful. This suffix implies "full of" or "characterized by".

Exploring Other Suffix Options

Now, let's examine why the other options are not suitable for all the given words.

Analyzing Option 2: The Suffix "-able"

Applying the suffix "-able" to the words:

• Use + -able = Usable (meaning: able to be used, correct)
• Truth + -able = Truthable (This is not a commonly recognized or grammatically correct English word.)
• Care + -able = Careable (This is not a commonly recognized or grammatically correct English word.)

While "usable" is a valid word, "truthable" and "careable" are not standard English words. Therefore, "-able" does not match all the words.

Analyzing Option 3: The Suffix "-ing"

Applying the suffix "-ing" to the words:

• Use + -ing = Using (meaning: present participle of 'use', correct)
• Truth + -ing = Truthing (This is not a standard English word in the context of creating an adjective or noun from 'truth'. While 'to truth' can be used informally, it doesn't form a common word like the others.)
• Care + -ing = Caring (meaning: present participle of 'care' or an adjective meaning 'displaying kindness and concern', correct)

While "using" and "caring" are valid words, "truthing" does not fit the pattern of forming a widely recognized word in the same manner as "useful" or "truthful". The suffix "-ing" primarily forms present participles or gerunds, and does not consistently create a new adjective or noun from all these words in a universally applicable way.

Final Suffix Selection for Use, Truth, Care

Based on our analysis, the suffix "-ful" is the only option that successfully creates a valid and grammatically correct English word when appended to Use, truth, and care.

Thus, the suffix "-ful" is the correct choice as it matches all the given words: Use, truth, and care.