This knife cuts very well. 这把刀很锋利。

(1) 改为否定句
—> This knife doesn't cut very well. 这把刀不太锋利。

(2) 改为“这把刀根本没办法切东西”
—> This knife doesn't cut at all.（句型 not...at all 表示“根本不……”）

(3) 改为 Do you think...? “不认为”开头的疑问句
—> Do you think this knife cuts very well? 你觉得这把刀锋利吗？

ABC department store is having a sale this week. ABC百货公司这星期正在大减价。

(1) this week 改为 last week
—> ABC department store had a sale last week. ABC百货公司上星期大减价了。

(2) 改为疑问句
—> Is ABC department store having a sale this week? ABC百货公司这星期正在大减价吗？

(3) 改为以 when 为开头的将来时疑问句
—> When will ABC department store have a sale? ABC百货公司什么时候大减价？