For each of the following locking protocols, assuming that every transaction follows that locking protocol, state which of these desirable properties are ensured: serializability, conflict$-$serializability, recoverability, avoid cascading aborts. $1.$ Always obtain an exclusive lock before writing; hold exclusive locks until end$-$of transaction. No shared locks are ever obtained. $2.$ In addition to $(1),$ obtain a shared lock before reading; shared locks can be released at any time. $3.$ As in $(2),$ and in addition, locking is two$-$phase. $4.$ As in $(2),$ and in addition, all locks held until end$-$of$-$transaction.