2)3) See the concept by yourself.
4) Company A failed to cancel the offer. One of the revocation requirements must reach the offeree before the offeree makes a promise. In fact, before he sent a telegram to the Hong Kong telegraph office, Company B had sent a telegram to the Shanghai telegraph office to accept the above quotation. Failing to convey the intention of revocation to the offeree before the acceptance by the offeree. So it can't be revoked.
5) The contract has been established. The key to the formation of a contract is that the promise made by the offeree reaches the offeror. At 3: 20 pm on the 22nd, it was delivered to Company B, and the contract was established.