let down: 使...失望
I feel let down by his indifference.
他的漠不关心使我感到失望。
He won't let you down; he's reliable.
他值得信赖，不会让你失望。

aggressive: 主动地
His style of argument in meetings is not so much aggressive as pertinacious.
他在会议上的辩论态度并非锋芒逼人而是坚持己见。
Red fire ants are very aggressive and readily attack anything that disturb them.
红火蚁攻击性强,容易攻击任何干扰它们的生物。