Answer:
C. didn't suspect
Step-by-step explanation:
In the passage, the part saying “didn’t suspect” is wrong. The story is proposing the plan which should be in the future. All the rest of the passage uses future simple tense – verb to be in the future form (will) and the verb in the infinitive.
“Didn’t suspect” is written in the form of past simple tense. This tense is used when some event has already happened.
As the surprise party did not happen yet, but will in the future, this part has also to be written in the future simple tense.
The correct sentence should be ”He won’t suspect a thing”. Won’t is a short form of will not – a negative form for future simple tense.