Step 1: Understanding the Question:
There are three blanks. The first blank needs a word for a disease, since the sentence says "in a case of acute ______", and only a condition, not a body part, can be described as "acute". The other two blanks need the adjective "mucous" and the noun "mucus" placed in the right grammatical slots.
Step 2: Key Formula or Approach:
"Sinus" is a hollow space inside the skull bones, a body part, not a disease. "Sinusitis" is the disease in which the lining of the sinus becomes swollen and inflamed; the suffix "-itis" itself signals inflammation, as in arthritis or tonsillitis. "Mucous" is the adjective, used to describe a membrane, as in "mucous membrane". "Mucus" is the noun, the thick liquid the membrane produces and secretes.
Step 3: Detailed Explanation:
The phrase "a case of acute ______" needs a disease word, so it must be "sinusitis", not "sinus"; this immediately removes the first three options, which all use "sinus" here.
The second blank describes the type of "membranes", and since membranes are being described, the adjective "mucous" is needed: "mucous membranes".
The third blank is what those membranes "secrete", which is a substance, the noun "mucus", not the adjective "mucous".
Putting these together, only "sinusitis, mucous, mucus" fits, which is the fourth option here.
Step 4: Final Answer:
The completed sentence uses sinusitis, mucous, mucus, which is option 4.