challenging

"The Y chromosome has many sections that repeat, and even some that are palindromes -- the same forwards and backwards. It makes it challenging to understand which genes are encoded there," Cothran explained.

“When we’re really emotionally stimulated, it makes it so much more challenging to have civil conversation. For politicians, I think that’s powerful, because emotions can be very easily manipulated.”

“We have to deal with them, and absent the ordinance, it would be challenging for us.”

He acknowledged that stopping people-smuggling gangs was "an incredibly complex and challenging problem" but said he was aiming to disrupt their business models.

However, because air in the boundary layer interacts with land, the ocean, and everything else at surface level, modeling it is especially challenging.