When you reply to an email, Mail app for iOS by default will quote the whole email text in your reply message. Often you might want to highlight only selected text in your response, in order to give a focus context in your reply. Luckily there is a quick way to achieve this.
Open the email message in Mail app. Select the text by tapping on the text area and drag the highlighter to the desired selection. If the selected text includes a photo, it will be included as part of the quoted text in the reply.
Tap the action button and select Reply in the pop up menu. The reply message will come up with only the selected text quoted.
The above illustration is using Mail app for iOS, but this shortcut will works in Mail app for OS X too.