この問題はとても難しい。

this (something or someone close to the speaker (including the speaker), or ideas expressed by the speaker)

question (e.g. on a test); problem; problem (e.g. societal, political); question; issue; subject (e.g. of research); case; matter; question (i.e. doubt); public discussion; controversy; trouble; problem; inconvenience; difficulty

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

very; awfully; exceedingly; (not) at all; by no means; simply (cannot)

difficult; hard; troublesome; complicated; serious (disease, problem, etc.); fussy; particular; fastidious; hard to please; displeased; gloomy; glum; sullen; serious (look); dirty; unclean; filthy; detestable; unpleasant; uncomfortable; creepy; spooky