If people eat natural poisons by mistake, they ________ go to hospital without delay.

My sister met him in the hospital yesterday afternoon, so he _________ your lecture.

 —Listen! Is that Pingping playing the guitar?  —No. It __________be Pingping. He has gone to Beijing.

(2010·辽宁高考)Doctors say that exercise is important for health, but it ________ be regular exercise.

--Whose tennis racket is this, Linda?--Look! Jerry's name is on it! It _________ be his.