Step 1: Identify the sentence type.
This is a Type-3 conditional sentence (unreal past condition) used to express regret or hypothetical situations in the past.
Step 2: Applying the correct structure.
The correct structure is:
"If + past perfect, then + would have + past participle."
Here, "Had I known" is the inverted form of "If I had known", so the second clause should be:
"I would have attended it."
Identify the part of the sentence that contains a grammatical error:
Each of the boys have submitted their assignment on time.
Rearrange the following parts to form a meaningful and grammatically correct sentence:
P. a healthy diet and regular exercise
Q. are important habits
R. that help maintain good physical and mental health
S. especially in today's busy world