( 1)a

(2) It is beneficial to remove benzaldehyde from the product.

(3) Check the air tightness of the equipment? Balance the air pressure and check whether the equipment is blocked.

(4) the liquid becomes colorless and transparent

(5)dcba

Test analysis: generally, the water flow in the condenser tube is from bottom to top, that is, from A to B; (2) converting low-boiling organic matter into high-boiling organic salt, and then distilling to remove benzaldehyde impurities; (3) Check the air tightness of the equipment before it is inflated; The function of the glass tube is that water enters the glass tube when the pressure in the container is too high, and water enters the container when the pressure is low, so the function of the tube is to balance the pressure and check whether the device is blocked; (4) After the benzaldehyde is completely distilled, the water condensed in the condenser tube is colorless and transparent; (5) After decolorization, the activated carbon is filtered out to obtain its salt solution, and then acid is added for acidification to obtain cinnamic acid crystal precipitate, which is cooled, filtered and washed. If the purity is not high, it can be extracted by recrystallization, so the order is dcba.