If I leave you, you’ll die. You can’t see me, until it’s cold. You can hold me, and I can be taken away, but your hands can never grasp me. What am I?

Breath

Explanation:

If your breath leaves you, you die. You can see your breath when its cold. You can hold your breath. Someone can take hour breath away.

oxygen because without it we will die and when its cold we can see it

not concrete, existing in thought or as an idea but not having a physical or concrete existence

sentences vary by structure as well as by function. there are compound, complex, and compound-complex sentences.

simple sentence

i like to read.

a simple sentence has one independent clause.

compound sentence

i like to read, and i also like to write.

a compound sentence includes more than one independent clause, connected by a coordinating conjunction (and, but, for, nor, or, so, or yet).

complex sentence

i prefer to read books that are bestsellers.

a complex sentence includes one independent clause and one or more dependent clauses. (a dependent clause is one that cannot stand alone.) types of dependent clauses include relative clauses (i kicked the boy who pinched me), adverb clauses (i am going home now because i have a curfew), and noun clauses (i don't know what to do next).

compound-complex sentence

although i prefer to read current bestsellers, i do like to read old agatha christie mysteries, and i also like some 20th-century science fiction.

compound-complex sentences take a bunch of clauses (multiple independent clauses, and one or more dependent clauses) and toss them together like a salad. although these sentences take practice to write in a grammatically correct fashion, they can hold a tremendous amount of meaning, and are common in academic writing.