State Department Spokesman P.J.Crowley said the United States welcomes the visit by President Lula, but that it is doubtful it will yield anything useful.

VOA: standard.2010.05.14

She took a doubtful step and then undid it To raise herself and look again.

她犹豫地踏出了一步又收了回来,又上去继续往下看。

耶鲁公开课 - 现代诗歌课程节选

However spokesman Crowley said interaction between Clinton and her Iranian counterpart in Kabul is doubtful.

VOA: standard.2010.07.16

"Well they certainly will be doubtful of it unless President Obama makes a strong argument.

VOA: standard.2009.09.22

Stephanie Pines was doubtful another future bid would have the same support from such notable figures as talk show host Oprah Winfrey and President Barack Obama.

VOA: standard.2009.10.02