Learn English – Shall I use have forgotten or forget in this sentence

I find this above chart quite helpful in understanding tenses and the period of time they refer to in order to accurately choose tenses to use in a particular sentence.

First Q1: Present continuous tense is used in this sentence since the river is flowing continuously for the whole of ‘today’. Simple present should only be used in this case if the time frame (today) wasn’t given because only then would the sentence be a generalizations. e.g. The river flows. (Generalizations can't be specific so you can't specify a specific time period)

Q2 This is an example of a generalization. In that sentence, you’re generalizing that you usually or always grow vegetables in your garden. However, this year is an exception since you aren’t growing any vegetables. ‘Aren’t growing’ is in present continuous to express how throughout this year, you are continuously not growing any vegetables in your garden.

Present continuous tense isn’t necessarily used to name exceptions to a generalization. Sometimes past continuous can be used as well. (Daniel usually runs around in school but yesterday he was limping since he injured his thigh)

Second: Your method of using present tense instead of present continuous also works if you want to phrase it as a generalization. The present continuous form is probably the right answer because of the question requirements.

The main difference between the two is that present continuous is used to refer to a specified period of time between the past and the future while simple present is used to generalize throughout an unspecified period of time (has been happening since forever and will continue to happen forever)

Third: Similarly, you can use both present continuous and simple present here (Is anybody sitting there? vs does anybody sit there?). However, I would think that simple continuous is more appropriate in this case. If you look carefully at the chart, present continuous extends a bit to a specific point in the future as well while simple present is just 1 point in the timeline. Therefore ‘Is anybody sitting there?’ would mean ‘Is anybody sitting there now and will anybody be sitting there before the movie ends?’ (The period of time referred to here is from the present to a point in the future (ending of movie)).

In this case, simple present (generalization) means ‘Has anyone sat there before and will anyone sit there in forever’ obviously, since this is a movie theatre seat, someone would have sat there before your movie and will be sitting there after your movie. Thus, the answer to that question if it’s in simple present would always be ‘yes’ regardless of whether anyone is sitting in that seat during your movie.

Therefore, I would highly recommend using simple continuous in this case.

"So far" means "up to now", which is what the present perfect continuous also means. So they go together nicely.

My bike has been running smoothly so far. I hope it'll make it through the end of the week without needing to go to the shop.

That being said, the simple present is fine in the context of your second sentence:

John: Hey Subha, how's your day going?
Subha: It's good so far.