Both are usable depending on the context: "These/those are the plural forms of this/that, and behave in the same way. As a determiner 'this' is used to identify a specific person or thing close at hand or being experienced. As a determiner 'that' refers to the more distant of two things near to the speaker, or to a specific thing previously mentioned."
It's funny to me that German is less complex in this case, when when it's more complex in a lot of other cases :-)
Incidentally in German many adjectives are the same as the adverbs except they are not modified and quite a few native German speakers don't explicitly realise this. This explains why some with intermediate level English have problems choosing between eg. slow and slowly when speaking English.
Yes, sometimes it can be a bit hard to pick up the individual words. Learning the spoken cadence and inflection of a foreign language can be difficult. Sometimes I have to listen several times or slow down the audio. I find it also helps if I listen to German for a few minutes--the Tagesschau.de videos are useful--even though I don't fully understand and can't keep up.
And, of course, the computer-generated audio is not perfect. So, the listening lessons will always be a bit problematic, but not insurmountable.
As for a
ktive rather than a
- without the definite article (remember, you misheard sehr), the adjective must be inflected. This is referred to as "strong inflection".
- neither "a
ctiven" nor "a
ctive" are German words.