I am a college sophomore with double majors in mathematics and microbiology. I wrote this email to seek your advice on selecting a theoretical, proof-based textbook on the multivariable calculus. I will be taking a multivariable calculus on this Summer but it unfortunately is a computational one with little theories. I would like one that comprehensively covers the theories of multivariable calculus and perhaps including sections on the applications too (but not necessary). Couple of textbooks I have in my mind are ones written by Serge Lang, Apostol, Marsden, Hubbard, and Fleming. Which one is good for self-learning?