The 太脏 Word Bank tile is silent, they always stay silent for the entire lesson. Defective network code? What a headache. Reported [The audio does not sound correct] 2019 June 13th Thursday Opera 60.0.3255.141 Mac OS X 10.11.6 64-bit.
One of these days I'm going to know instinctively when a 了 is needed (and where) instead of needing to check every time.