Problem solved for ex16.1, correct answer is
EntityValue[Entity["Country", "Switzerland"], EntityProperty["Country", "Flag"]]
It seems for ex16.1, the system really want "everything". I used "Flag" for second argument and the checker marks it as "incorrect" (only for ex16.1)
EntityValue[Entity["Country", "Switzerland"], "Flag"]
I believe the exercise is to recognize the first argument is an "Entity" and the second argument is an "EntityProperty". However, I want to mention that for later ex16.x, the checker does not want "everything". For example in ex16.4, the correct answer would be
BarChart[EntityValue[EntityClass["Planet", All], "Mass"]]
but if you use the "everything" involved code as in ex16.1 (by changing "Mass" to EntityProperty["Planet", "Mass"])
BarChart[EntityValue[EntityClass["Planet", All], EntityProperty["Planet", "Mass"]]]
the checker will mark it as "incorrect".
Something more about ex16.x involving "Species":
There is a high chance that control= will direct you to the correct animal, but "incorrect" InputForm that the checker will mark it as "incorrect". For example, in ex16.13 (the last ex16) control= "koala" gives me the koala picture as the desired output. When I copied the code here, it shows the following
ImageAdd[Entity["TaxonomicSpecies", "PhascolarctosCinereus::2kft4"]["Image"], Entity["Country","Australia"]["Flag"]]
In the notebook, Entity["TaxonomicSpecies", "PhascolarctosCinereus::2kft4"] will be compressed as a orange box with text "koala species specification" because I used control= to made the input.
However, the system is asking for the exact input as
Entity["Species", "Species:PhascolarctosCinereus"]
I believe they point to the same species datapage. The first try by control= is marked as incorrect (at least in my interface). Weird.
A similar issue happened for Ex17.6
When I used control= "2500yen", the nature language process returns
Quantity[2500., "Yen"]
However, the checker wants
Quantity[2500, "Yen"]
I do buy statements from Phil that redoing those exercises to explore the possibilities will enhance my memory and understanding of the Wolfram System. But at some moments, I found ex16.x is just not doable because of the nature language processing, I can do nothing about it.
I solved my problem about those syntax issues using with exercise solutions for 2nd-edition of the book.
https://www.wolfram.com/language/elementary-introduction/2nd-ed/answers-to-exercises.html
Ex9.7 and Ex14.7 does not work, the solutions are wrong in the sense that the output is not the same as desired output (does not satisfy the question)
BTW, I encountered some errors simply due to the name of variables.
It seems the checker prefers
n in Table;
i,j in 2-dimensional Table;
x,y,z for coordinates;
r for radius;
theta for angle between (maybe) {0, 360 Degree};
x Degree for x between (maybe) {0,360};
or use the variables named by the question
For Manipulate, click the + you can see the name of variable as the name of control bar