Both *sound* correct to me, but according to a website that I found, 4 is correct. Is that what your book says? The website says, "To indicate two future time-related activities, a verb with future tense in the main (matrix) clause ["you will see the lake"] is followed by a preposition [actually, a subordinating conjunction] with a present-tense clause as its complement." ["as you approach the hotel"] From: http://www.grammar-quizzes.com/8-5.html Their example: "We will pay our bill as dinner ends."

I can see this getting complicated :) However see this from http://grammar.about.com/od/pq/g/progtenseterm.htm (Progressive aspect is) a verb phrase made with a form of be plus -ing that indicates an action or condition continuing in the present, past, or future. A verb in the progressive aspect (also known as the continuous form) usually describes something that takes place during a limited time period. ... "A progressive form does not simply show the time of an event. It also shows how the speaker sees the event--generally as ongoing and temporary rather than completed or permanent." (Michael Swan, Practical English Usage. Oxford University Press, 1995) "As you are approaching the hotel, you will see the lake" seems to me to be an example of a verb in the progressive aspect. On-going and temporary. To me 2. not only feels right, I think it is. However I agree with Peachey - keep it simple (literally and grammatically). So 4. is better.

I agree that 2 and 4 sound correct.

I agree with Alan's research: because one clause indicates a time, you keep that in present simple tense. No conjugation, otherwise that's just plain confusing. "As you approach the hotel, you will see the lake." Pretty straightforward.

yes you are correct. 2 and 4 are correct answers.