Translation:There are four pictures.
I'm getting toward the end of the tree, and it doesn't look like there are going to be many more introduced. That, along with the at least two readings for most kanji, is to me the most irritating aspect as well. It's not limited to Japanese, though, so you might not want to do the Vietnamese program either, or Korean when it comes online. Swahili has what to me is an even more irritating system, in which all the verbs and adjectives also change based on what classification a noun is in. I do find, though, than when you master such a system, what was an irritating feature can come to be one of the most charming features of a language.
That's a great question. I just e-mailed my sister in Japan to see what she would do. OK, so she says there is no real default, but she usually gets away with "hitotsu, futatsu..." the tsu counter, which is for objects that fit the other categories. She says that, since it uses the Japanese, rather than Chinese, pronunciation of the number kanji, it's often taught after the other counting words, though.
https://en.wikipedia.org/wiki/Japanese_counter_word There are a large number of counters in Japanese. Even native speakers don't know how many they are. But It is not needed to memorize all of them. Some in the list are not used commonly.
It would be great if there were a "My answer should be accepted" option for the listening exercises. It's frustrating that certain kanji or kana spellings aren't accepted in the listening exercises, and there's no appropriate option in the Report menu to correct it. I prefer typing over using word banks when possible, but most of the time, the typed solution isn't accepted if it doesn't match the word bank spelling exactly, even if the same kanji have appeared elsewhere in the course.