Marker to use before Tsuki

I'm not very far into the course, but in Lesson 1.3 “At the sushi bar”, the first sentence used is "osushi wa tsuki desu ka?". But in grammar lesson 1.6 “To Like or Not Like”, they say that "tsuki" always goes with “ga”. Is this an error on the part of the course or is there a reason for it?

こんにちは (Konnichiwa) Kieran150,

Good question! 

Firstly, be sure to pronounce the word “like” as すき (suki) NOT つき (tsuki), as this means “moon”!

Most of the time, すき (suki) is used with the identifier particle が (ga) to IDENTIFY the thing you like, however, it can also be used with the topic particle は (wa).

This は (wa) is used to show CONTRAST, and highlight the thing that you like in comparison to something else.

For example, if someone asked you what fruit you like, you could say either りんご　が　すき　です (ringo ga suki desu) OR りんご　は　すき　です (ringo wa suki desu).

The sentence with は (wa) allows you to contrast your love for apples with other fruit and imply that you like apples, and not any other fruit.

You can read a little more about the use of は (wa) to show contrast in this lesson:

https://app.rocketlanguages.com/members/products/5/lesson/5045

I hope this helped! Please let me know if you have any other questions.

勉強を頑張ってください！ (Benkyō o ganbatte kudasai!)

In the example that Emma gave about liking fruit, both are appropriate answers.  

What fruit do you like?

りんご　が　すき　です (ringo ga suki desu).  I like apples.  Perfectly correct and standalone.  But what if you really hated oranges, or were allergic, or whatever.  

りんご　は　すき　です (ringo wa suki desu).  I like apples (but not some other fruit).

It is good to ask questions, especially if you're not certain about something.  Keep in mind though that especially with the audio lessons, they've only about a half hour or so to teach everything that they want to teach you, and might touch on grammar concepts that haven't been brought up yet.  Do the best that you can, and those wrinkles will get smoothed out (eventually)..  We hope.  For instance, I know in the audio lessons they use some plain language, which isn't brought up in Grammar lessons until Chapter 6.

Good luck, and stick with it.