Hello Pinki,
In answer to your question, first let me explain the difference between these streams, starting with
Botany
Zoology
Biomedical sciences
Now you need to understand is that, All the above three fields are very important and have a very good scope in future.
But all the streams are very different from each other as one deals in plants, other in animals and the third one in medicines so, firstly you need to evaluate what excites you the most was choosing botany will lead you into agriculture and that has a very good scope in future. Selecting zoology willing directly make you a doctor of animals. Opting for biomedical science will lead you into pharmacy and you know how composition some medicines are made and how medicines are useful for Healthcare.
See you need to evaluate your interest that in what particular field you be doing good because knowing what is best is temporary and building a career upon interest is permanent.
What is best among these three will not help you, but building a career based upon your interest will be the key to success.
My advice to you is, first know your interest and strength and based upon it choose your career wisely.
Hope this helps,
All the best
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