Answer:
D. A waiter can get a good tip if they are pleasant and helpful
Step-by-step explanation:
A.Where is my practice if they want to be able to carry heavy trays without dropping them.
Incorrect grammar and sentence topic is lost.
B.Since uniforms are required for this restaurant, waiters need to Buy it.
Incorrect use of capitalization and the it should be a "them".
C. If waiters aren’t too much of a hurry, you get a fin customers by being to abrupt.
Sentence is unclear.
Therefore the answer is A.
Have a great day!