Step 1: Understand the idiom.
The phrase "to kill two birds with one stone" means accomplishing two objectives by performing a single action.
Step 2: Apply meaning contextually.
Example: "By cycling to work, I get exercise and save on fuel — I kill two birds with one stone."
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