Point out the disadvantages of studying the grammar of a language at the level of sentence alone.answer in detail
Consider who learns a language the most quickly - and how.
Babies - by immersion in the world of listening and talking. It starts with repetition and word association and gradually progresses to stringing sentences together. Once understandable simple sentences are formed, new nuances of grammar are slowly added: prepositions and adverbs (adverbs of frequency and time are hard to grasp for young children, 'yesterday' can mean anything in the past and 'tomorrow' usually means sometime in the future), pronouns (also difficult - children speak in the 3rd person for a long time).
In order to learn a language (to be able to speak it or write it) all that is truly necessary is immersion in it and a desire to communicate. Grammar is understanding how the language works, which is not in fact necessary for speaking and arguably, not necessary for writing either, assuming a person is able to write what they can speak.
The biggest disadvantage of teaching grammar isolated to sentences is that it doesn't show the big picture of what is being built - the language as a whole. I like to say that English and math are actually much more similar than most people give them credit for. Sure, in a huge equation - knowledge of the basic functions of math are necessary - but when attempting to solve a complex equation, you need to know more than simply how to add, subtract, multiply and divide. Simply put, it isn't enough.