Is this sentence a simple, compound or complex? tania let her borrow the ipad, but she asked her to be careful.

Tania let her borrow the ipad, but she asked her to be careful is a compound sentences because of the use of 'but'. Whenever you use but, and or so in a sentence, you are writing or stating a compound sentence since you are joining with such conjunction two independent clauses.

d. because santiago thought any sharks would assume the marlin was part of the boat